I find that there are only a few "must-have" social projects on each planet. The rest are "nice-to-have", and I only really want them on my best planet. I have my good planets build "nice-to-have" while my worse planets build the "must-haves". If I have nothing to produce on most of my planets, I rush-buy the "must-haves" on the planets that are behind.
The must-haves:
- terraforming (anything with +PQ)
- +production (manufacturing center, etc; helps the planet catch up)
- banking center, economic exchange, stock market, stadium, teleporters, entertainment network (basically, all the ones that give +economy or +morale for a good upkeep)
Controvesial:
- research buildings; I find that the free research gives me more than the upkeep cost, even on poor planets. Some people will disagree with this. When you have lots of research buildings, you have to adjust your spending sliders; it's still a good deal.
Nice-to-haves:
- influence buildings;
Nobody builds propaganda centers. For cultural resistance, building an influence starbase is cheaper, and you can pull constructors from other sectors. The upkeep of 4 isn't justified by +5% morale.
Only build shipyards on high-PQ planets that will be producing combat ships.
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However, since rushing costs 10x as much as normal production, you really don't see a benefit to rushing unless a planet is WAY behind.
I usually just leave the backwards planets as they are. They generate some research and the occasional constructor, so they're still worth it. I also build +production starbases if I want to help a planet catch up, but you're better off maxing out your top planets first.
I find "wasted resources" force micromanagement to avoid it.