Yes, the waiting time is not the issue, it's the cash upgrade that is the problem.

Personally for me it's also a micromanagement issue. A lot of times you can't really squeeze in more with just one tech improvement.

Also it is a waste of effort to redesign every tech improvement.particularly when tech research is fast and manfucturing is slow.

I find myself designing Fighter II, Fighter III, setting my governers to change from fighter I to II to III, but in the end I only see Fighter III coming on line, but no fighter II, because none of my colonies finish Fighter II, before I started yet another new design.

In my rather limited field of expirience, I often find that if I make a minor achievment (such as getting laser MkIV) it's not worth the time and money upgrade everything, or if the weapon/defense in question won't make a difference. but I DO make a new design of the same ship, but with the new weapons or armor, and classify it as MkII or whatever, but I don't upgrade all my ships right away, unless I am at war and need that new weapon on the front line ASAP. However, if it is the last in a series or something, or if it is a major acheivment (miniturization, which allows me to put more stuff on)or if I find that it is better to go down a different line for the time being, I find that it helps to upgrade a little at a time.

I often have several 'marks' of a particular ship once it is finally rendered obsolete for good. A perfect example of this is during my first game, I found that I had many weapons of moderate quality, but I coulden't fit quite enough of what I had in mind on a single hull (I hadn't researched the bigger hulls yet), so I took a cargo hull, added about 2 pnts of armor for everything, and slapped my new weapons on there. Viola! Gilgamesh MkI Battlecruiser. (Of course, it was rendered obsolete once I got the larger hull designs.

As long as I have enough ships to defend all my planets from sneak invasions, I don't build many fighters with every new tech.

Maybe 1 or 2 if a planet has high production and I'm not cranking out constructors.

I ususally build a couple of the first tech fighters, then don't build others until some civ declares war on me cause my military is weak, then I switch every planet to building the most up to date fighter I can design, and procede to capture a few planets before making the warmongers pay heavily for peace

However, if you don't have a distinct tech lead and good production planets, it's usually a better idea to keep your military rating high with more ships early, to prevent that war in the first place

In the initial colony rush stage, I built single beam fighters (tiny hull, no extra engines) to keep in orbit of all my planets to discourage invasion. After a time I designed a better fighter (3 mkV lasers) and wanted to see what the upgrade cost would be (there were about 50 of the lesser birds built). I was astounded to see the cost was 100,000+ BCs and my treasury was still under 10,000 BCs at the time. Since nearly every one of those craft were in orbit around a planet, I guess upgrade COST is not based on distance from a planet.

Cheers,
Reaver

Upgrading fleets frequency depends on 3 things: new techs, cash on hand and need.

New Techs
Most people play with a "normal" or faster research setting. If this is the case you might be upgrading every 2 to 3 techs researched because you litterally will not have time to build a new version in the time you've researched a better component. If you are playing on a slower research setting, then you may find yourself deciding to upgrade more often because it's going to be a while before the shiny gadget gets better.

Cash on hand
Fairly straight forward. If you have the cash, go ahead and do an "upgrade all." I've had this cost as little as 4,000bc for new engines (~70 ships) and as much as 50,000bc for new engines, weapons and defense (40 ships). If you don't have the cash, but the new tech does improve your ships, there's nothing wrong with updating the design and having the new tech on new ships. (Unless you are researching a new weapon every 3 turns it's usually a benifit to have the new tech on your ships as soon as possible).

Need
Let's face it, if you are mopping up the known universe with Laser II, I don't think there's a need to put Laser III on your ships. On the other hand, if (like me recently) you start a war against someone with a better military (not just bigger...better weapons, or both) you never know... That space saved with the new tech may allow you to put another weapon, or defense on your ships.

I have been known to upgrade light fighters to medium fighters because some change in technology allowed me to add defense. When another change in technology allows me to put on two weapons, then I upgrade to heavy fighters. Of course, for the steps in-between when you have an opportunity to improve a weapon, or a defense, but not enough to change your ship class (light/medium/heavy), that's when you have to evaulate between the frequency of new techs, need and cash on hand.

I NEVER upgrade existing ships if there are more than three of that ship type. It's too expensive to be worth it.
However, I redesign ships after about three applicable ship components become available and have my planets switch production to the new type. The trick is to make sure that the new generation has the same speed as the old, or to design a completely new ship. Once an old class of ships become obsolete, I decommission them.

I'm a huge fan of experienced "Elite" units so I rarely decommission ships. A fleet of small hulled ships can do some impressive things if you keep them upgraded and allow them to accumulate enough experience so they have more hull points than a large hull.

It's even more important if you are not going for a conquest victory and want to keep your fleet to a minimum. Even if you are not involved on a lot of battles. If you keep using the same ships over and over they will gain experience quickly becoming more powerful than several green units of the same class. This allows you to keep your forces small but powerful at the same time.

Yeah.... Unless they have insane experience, I don't upgrade older ships either, unless I have very few of them. I use them as shock troops instead. I throw them at an enemy fleet to break it up a little bit, get rid of the older ships in a useful way and weaken the enemy just before I send in the latest and greatest to mop up.