There are, in essence, three types of invasion.

One: You see a minor and you need that class 15 world, because you're on rare/rare habitable/planets or whatever the case may be. You get in and out fast, and you build what you can on it because you need the real estate that badly. Incidentally, it also frees up the three mining resources they just so happened to get within 5pc of their homeworld.

Two: War. In general, you're probably not going to want to bother to build up worlds you take from a major. Your best bet is probably 2 factories to get production up and then just fill them with stock markets. You should already have a decent production base with your core worlds, and if you still need vast amounts of research, then maybe you shouldn't be fighting this war yet.

The above needs to be modified if you're fighting a major within the first 6 months or less, and/or if you're playing with all 9 of them, as the former worlds of the first AI or two become your "core" worlds.

Three: Cleanup. You're taking worlds because they're left. You're down to the last AI or two, surrenders are disabled because although you aren't playing the Korath, you're playing a Spore mentality (MUST...KILL...EVERYONE), and everything but military victory is turned off so you can do so. At this point, it really doesn't matter WHAT you do with these worlds. Stock marketing them will help your economy some, which will help your score some...though not much.

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Generally by the time I'm at war I've gotten all of the research I -need- done, though maybe not all that I want...and this does change a little from game to game. So when I take over a planet with 12 discovery spheres on it with a tech capital...well, if the tech capital is there I might keep it, but in general, I'm not running a very high research rate at that point anyway, probably 25% at best. So in most cases I decommission all the spheres-can't do so with the tech capital, IIRC, but what are you gonna do?

I try not to decommission too many factories, though the problem that creates is helped by DA having an Old build list as well as a New one. I like to keep at least 3 or 4 (if they were there to begin with) on the planet for when I decide I want to build something on it again.

There have been games where I decommissioned the starport on some planets, but that was before I realized you can't rebuild it if you do that...so I don't do that anymore, for the most part.

Thing I've started doing when that happens is keeping a few quick ships on hand (custom colony or troop ships) to ferry some population over there and get it paying for itself quick without having to worry about pop. growth.

ed. Also has the bonus of preventing a quick sneak attack with a single transport from taking the planet back immediately

The first thing you might want to do is invade with a greater number of troops, this will give you a greater post-invasion population, which will help that planet's economy. What i do after an invasion is immediately buy a fetility clinic to get the planet' population up faster, they only cost like 240 (of close to that). Its the loss of population that caused the negative income of the planet. I never decommission any improvements, all of my new planets become part of the machine. Especially since planets that are invaded are more likely to be closer to you next target than your older planets.

I will build over some tructures like morale or influence buildings, fleet managers, fusion reactors and all but one farm; it depends on what the AI built on that planet.

Usually the negative income from a new plant isn't enough to take don an economy. If he -42 bc was too much for your economy, I think you need to work on your economy more. I guess if its REALLY late in the game and teres not much left to research you could get rid of labs and such, but they will still help your research score in the end.

One trick I like to do (when tech trade is on) is give all the minors your econ techs. They tend to focus on building econ capitals when you give that option to them. Then when you capture the planet, you get an additional econ capital. Just make sure you build, or are building, your econ capital before capturing theirs.

If they have one built, the planet will usually be in the positive cash flow side of things.

Only problem is by the time you build a No Mercy Invasion Center, you can usually afford the invasion costs.

More growth. If your population is already maxxed in your home colonies (and they ought to be for most planets) transporting colonists to new planets effectively doubles your growth rate.

Moreover, getting colonies past the critical 1 B population mark is often key - using new people to help get the 1B base off the ground is faster than if you just leave the planet to itself.