Really interested in your post darvin3 as i had an idea for a while that may work.
One flaw of the game was that, even if it considers itself as a 4X game, it lacked depth in civilization building : you upgrade all planets the same way and once you are done, you will focus only on the military.
There is no way planets can be as customized as in GalCiv 2, that's impossible but GalCiv had the bright idea to create Galactic wonders (one for the entire galaxy), civilization achievements (one per civilization) and super planetary improvements (one per planet)
What about civ Techs that allow you to create these improvements in your planet ? Only one improvement by planet (or maybe two on high quality planets like terran ones) and the more powerful the improvement is, the more civ labs it will need to unlock the tech and thus the improvement.
I see it that way :
you click on a planet and next to tactical, logistic and population buttons, you have a planetary improvements button that display a list of planetary improvements that you can build ifyou have researched the proper tech before.
For example you can have :
super planetery improvements :
TEC : manufacturing center : + X % ship building speed on that planet
Advent : Mind focusing building : + X % AM regenerating in the gravity well
Vasari : Oppression center : + X % tax income on that planet
and so on...
civilization achievement : race specific, one per civilization : as wonders, they generate culture
TEC : large scale sensor arrays : allow them to see everything on planets next to a planet they own.
Advent : Temple of mind : ability cool down time - X %
Vasari : Repression agency : make this planet impossible to be culturally overcame
Galactic wonder : for all races, only one can be built
Galactic neutral ground : provides a neutral ground to all races for negotiating : + X % relationship bonus
Holy memorial : higly religious place where people from all races and civilizations come to pilgrinage : + X % culture bonus
Quantum buster theory : give your civilization an edge in quantic probability manipulation so your ship have now a X% chance to make a critical hit (damage x5)
Galactic wonders can't be destroyed but you can choose to destroy or to keep the enemy improvements when you take one of his planet.
They are only examples but you can make them powerful enough to give you a real advantage against a military-only opponent.
You can also imagine a condition victory where if you have 5 galactic wonders, you win.
I think it would be great but i don't think the devs has something that intricate in their plans for diplomacy release.