My 2 Cents on how to improve GalCiv3 with some simple changes:
1. No "end-of-turn-wait"
Do away with the "end-of-turn-wait". It is just tedious to press "next turn" again and again until at last the thing you are waiting for (ship is built, tech is researched, whatever) is finally done. The famous game "Master of Orion 2" had this option (no end-of-turn-wait) and it did indeed improve gameplay enormously, because waiting did not feel as tedious anymore.
The game will only stop if either a new tech is discovered, a ship or planet is attacked or if a shipyard or colony runs out of orders.
2. Race-specific music-scores
Race-specific music-scores for diplomacy, declaration of war and so on would be great. It would improve imersion in the game.
3. More equal starting positions; more than one planet at start
I think, every major race should have more than one colony to start with (e.g. three colonies instead of just one). It simply destroys game-balance if one (or more) major races end up in a desolate part of the galaxy with no meaningful chance to expand at all.
4. Give everybody a speed-burst
At the moment, ships are incredibly slow at the start of the game. Giving everybody a higher base-movement-speed (e.g. 4 instead of just 2) would make the game feel more dynamic. It would also speed up the discovery of the map.
5. Do away with "just dead" planets.
While I understand, that not every planet can support live on a larger scale, I think, that it is a disapointment for the player to discover yet another star-system with nothing but dead planets that are absolutely useless.
Why not give those "just dead" planets some purpose, as for example, a mining-colony, a gas-mine, a fleet base, a science lab, a space-factory or something else?
6. Fix the algorithm for planet generation
In my impression, extreme planets and outright hostile planets are rare, no matter whatever you chose as a starting setting. Even if you chose the amount of habitable planets to be "rare" and extreme planets as "abundant", there are always far more habitable planets than extreme ones.
In my opinion, it would be far more interesting if there were more "difficult" planets (toxic, radioactive, desert, frozen...) and less "run-of-the mill" habitable planets. This is especially true, because if that were the case, the trait "adaptable" would be valuable (which it is not at the moment).
7. Tune down (or abolish) star-bases
At the moment, star-bases are mostly a source of tedium. Noone really enjoys to shuttle 20 constructors to a star-base to built it up, just to have it destroyed by some small random fleet that happens to wander around.
What is more:
Star-bases seriously hamper the AI, because it is not able to employ them as well as a human player can. The AI tends to built either no star-bases at all or an insane amount of them (three econonic star-bases in the same star-system? Really?)