Just make it so that everything except for example starbases id deconstucted when tradeing a planet. Problem solved. As a sidenote, there could be tech that allows X random planetary modules and/or planet upgrades to be converted to the new owners equivalent.
You could do that...but that goes back to my original point, why would you ever trade planets? That is a ridiculous economic loss unless the planet had hardly any structures to begin with...
You sort of can already trade planets...you scuttle the planet, then allow someone else to colonize it...yes, you lose the investments made into planetary upgrades and the time it took to grow population...but that is likely comparable to the structures you would have lost if you traded the planet instead...either way, you lose a lot of money unless it is a very unique circumstance...
How is that sharing? If you sell them, you can no longer use them. Investing in research, production or other infrastructure and then "renting" it to other players for profit, protection or diplomatic advantage would actually add very cool new dimension to the game.
You are only looking at this from a SP perspective...in MP with human teams, I guarantee you people will abuse this...the vast majority of techs only require x number of labs to research the tech, but if you lose those labs, you still get the benefit....the only exceptions to this are prototype technologies (allow you to build structures, ships, and build/use superweapons)....techs like development mandate, allure of the unity, etc. don't have any prereq techs...so you could easily temporarily "trade" or "give" a planet with the appropriate research facilities to a player so they can quickly research that tech...then, once it's researched, they give the planet back to you or some other player...the AI may not give planets back but humans on a team will...
Very few players are actually researching in all the tech trees all the time in competitive MP games...this means that players could easily "pass around" the research labs, alternating between having a lot of civ labs and a lot of mil labs...you could put restrictions like, you can't make use of the traded facilities for x amount of time...but then why would you bother trading them if such an action penalizes both parties?
Your argument that it is balanced because everyone can do it only works in certain situations (mainly 2v2s)...in general, the map and starting positions dominate the course of the game and which/how many players go eco vs. frontliner...one team may easily be able to have 2 eco players while the other team can only safely have one player go eco...in this case, trading planets/research facilities gives the team with two eco-players a huge advantage...implementing this mechanic would not maintain game-balance, it would only accentuate the differences cause by map variability (which is entirely luck and gimps enough players already)...
Galactic Civilizations is a very poor example to use...in Dread Lords and Dark Avatar, all the factions have the same tech trees and improvements while in sins all 3 factions are very different...even if you are talking about ToA which does grant significant faction differences, that expansion is very unbalanced so I'd hardly use that as a good comparison...
GC II is a great SP game...but it's multiplayer doesn't compare well with that of Sins...
