One thing you didnt mention yet...but for sure most of you know about:
It happened to me quite often in my last games (even multiple times in one game), that
Class 0 planets get "available" through the Minors joining around mid/end-game! They seem to have the so called "Eden Device".

PQ rises from 0 to about 15, with further terraforming + soil enhancement even higher. Wait for them to build a ECO / MANU or TECH capital - make sure you got your transports parked nearby then

Give Minors a chance.. Let there be Class 0 planets

About the mining instead of generating resources class zero planets could generate a certain amount of money if you build something like a mining facility on them.

Good idea, like an unmanned mining outpost or something to that affect..

This happened to me by accident, i was trying to move a collony ship to a good planet and accidently clicked an empty (0) planet. It actually made a collony there but there were no improvement tiles. Needless to say the happiness of the planet was extremely low and i think getting lower. However since this was at the edge of my empire it actually opened a huge section of the galaxy up to my otherwise waiting colony ships which i exploited. But i didnt get to mess with that much since i was then attacked and pretty much wiped out. But im going to test this again on my next game.

The problem with the EDEN device (go go genisis power) is "Why dont we use this on colonies that we own already" and if you say because of the population think of the evil player for a second... or why not abandon the planet and then use the thing. No I think the best idea is to use the 0 class planets for:

1. mining
2. sensor outposts
3. waystations to increase the range of your fleets

yea, i agree with ya naustghoul, to me all the class 0 seem to be waste of space, i mean a few of them yes, but there are soo many even if u choose few planets etc. Giveing them some stragtic value will open up a much more deeper level of play (if thasts possible)

Just imagine for a moment if you got 1 or 2 more habitable planets per star system. Here now from a 15 planets per race game to 30 or 45 per race??? That would be rediculous and a long drawn out game of attrition. If you were playing a conquest type game you'd have 100's of planets to have to deal with each turn. Nope, bad, idea, leave the amount of planets like they are now or only if it's an OPTION. I like streamlined play, not a game that takes a month to play.

For me, it is essential for maintaining the illusion of 'reality' within my role of intergalactic leader, for space to be as 'space-like' as possible. This means lots and lots of uninhabitable space, dead-end planets, and the occasional gem in amongst them. Yes, class 0 planets are a waste of space which is how I like them as it stops the galaxy from appearing teeming with life and possibility. I much prefer a sense of cold bleak emptiness in the void - it appeals to my inner existentialist.

leave the amount of planets like they are now or only if it's an OPTION

From a Scenario Designer perspective this is a very good idea, as it gives the best of both worlds (pun intended), and is actually implementable now via editing XML file that controls how habitable planets are: say just edit this file and place it in the scenario "sandbox" along with a game scenario that has been designed, and "poof!" instant habitable planets all over the place!
Regardless, between all the empty space and the multitude of Class 0 planets I think the game needs to do something/ have some hooks available for Creators for both of these items to spice things up.

D

I think it would be good if some class 0 planets could at least have mines on them or on their moons.

exactly, they dont nessorily have to be habital, but lets say its a gas giant, you can have a orbital processor that turns some of the gas in to credits. Or on a unhabital rock would, you can use the raw materials for a bonus in ship product or credits...

You can do this just like you do with a starbase, have it to go unhabital planet and have an option of

A. Orbital Waypoint station (cheaper then a starbase, without weapons, but extends the range of your ships)
B.Miltary MINE (mines the raw resources and puts it to miltary production, has to be on a rock type world)
C.Social Mine (mines the planets resources and puts it to socal production, has to be on a rock type world)
D.Orbital Research outpost (team of researchers workin 24/7 can be put literaly on any planet)

Ideas:
Make some 0-class planets different, like Gas Giants, Toxic Enviroment, Wasteland and others
Constructor's improvements for different types, at first there can be built some structure like Work Station around or on that zeroclass planet and then it can be improved with this:
-Rare Chemicals Mine(Gas Warfare Cheaper or removed "decrease quality" factor + some bonus, available to build after some tech researched);
-Tourism base, ancient ruins(Like City in the Sky for Gas Giants and Valley of the Kings for Wasteland);
-Asteroid thrusters' facility(Transport asteroids for refining so +to social production and Mass drivers' suage cheaper)
-Hidden Research Facility - bonus to research at random branch of res.tree(can be discovered only with Sourvey module or Sensors II, otherwise marked as useless planet - they still should present, not everything can be put to use)
-Empire's Junkyard(only one allowed) - provide system-wide/Empire-wide morale and/or pop growth, can be trade good. Possible for wasteland-type zeroclass.
-Rare fuels(+1 speed in sector, Toxic type of zeroclass)
-Reabilitation base(For Good, Gas Giant) - Base wich privide help to people in need. +morale+pop growth in Sector it's built.
-Excavation Sites(Neutral, Wasteland) - Site in wich people observe remains of ancient civilizations and learn about them. +Economy/Trade.
-Labor Camps(Evil, Toxic) - Labor Camps, no more or less, dump all scum ofthe galaxy to dig uranium and refine chamicals. +Mil production+loyality.

-Operational Base(one per system, every type of zeroclass) - provide minor info about system's whereabouts(like minor spy level)
Upgrades. Not like I then II then... but I or II or...
==Upgrade I - Monitoring stations: Provide medium info(no further or spying would be useless)
==Upgrade II - Sector Command:Privide Info about sector i.e. reveal fog of war for entire sector it's build. Req ==Scanners II.
==Upgrade III - Patrolling Command: Add attack/def to our and allied freighters.
Suggestion for Eden device - it can be just improvement like ED stage I etc. until some stage is reached with some techs allowing to drive that improvements further. Example:
Early tech: 5 constructor ships required to reach final stage, allowed for the time beings. Can press something like "Initiate Terraforming" and get class 3-4 planet.
Mid-Tech: We know some Xeno farming and soil blah blah blah, can add some techs that make some logic and can now we can add up to 7-8 conships and get planet 7-8 as a result. Same with late-tech. Surely there must be "She's gonna blow!!!" option, representing chance of failure of planetforming - additional planed is a HUGE advantage to make it easy-gained so process should be expensive at later stages where planets of 5-9 class are expected. As well as option for autocolony for newly created planets.

double post

Love the idea that you have there Chelovek... hell I would love the idea of dropping my garbage on a 0 class world or racking in the dough from soft marks on a tour of the "Ancient ruins of Tuti-Fruti" on a toxic wasteland (I would charge extra for gas masks )

Why not have the class 0 planets only habitable to minor races?

I swear they're there for no good. 1-3 planets, and they're always complaining about my super-duper planet-sized battleship hovering over them.

Say their planets are class A0...not habitable by other races, but they can make good use of them. That way they're able to expand, but no one can "take over" the planet, only outright destroy it. Its they're own atmosphere type?

Then have a few class 0B planets able to do what Chelovek suggested?

There are 377 habitable planets on the gigantic map I'm playing right now. Habitable. If I had to worry about all those that AREN'T habitable, a sure case of insanity would set in. I realize that other players would be going insane with just the 377 habitable ones. I like moons being cosmetic, and starbases do the job well enough.

I would like to see multiple moons, though. Big ones, small ones, purple, green, all around one planet. Then planets with no moons or just one or two. Asteroid belts would be neat, reducing movement and interactive nebulae..

Asteroid belts would be neat, reducing movement and interactive nebulae..

They were planning this, but I think it became too complicated for the initial release. They might add this sort of stuff in later in an expansion, though.

Long has been discussed... I for one woudl ahev moved to a different planet classification system using the pq as a base. You can have kinds of planets like in Moo2 (SORRY for bringing it up but it's cool) and have it applied to the PQ. Example a small barren planet would be PQ4, medium Barren PQ5, large barren PQ6, small desert PQ7. And so on. You would develop techs that would allow you to convert one planet to anotehr. Like upping Barren to Desert, which would in a case os small barren move it from PQ4 to PQ7. And you could even have one tech that would increase your planet size! By maybe absorbing some asteroid field into it's mass or a moon. So a small planet would become tiny and so on. Except there would be no way to change the max sized planet up :/

THis is definately osmething 4x players want do to long history and the fun factor of empire building. You can look at a barren corner of the galaxy and say, "It's not much, but in 10 years this can be a paradise!" Which is what I did in Moo2. Finding a crappy system with 2 asteroid fields, 2 gas giants and one small radiated planet

Love the ideas Naustghoul, Chelovek. It could be setup as a starbase in the planet orbit. and use constructors as you said giving you starbase like attributes.