Not sure if picking just one aspect of the Moo2 research approach would be good for GalCiv3.
The MOO2 worked well because, while you were constantly research in all areas, you were forced to make a choice. Only Creative races (a very expensive perk) enabled you to get all techs at each level. The rest you had to capture, steal or trade for. This worked really well because you were forced to pick a direction for your race, either in your tech choices, or by putting sufficient investment (and research) into conquest, espionage & diplomacy to get the other techs you needed.
This approach also greatly improved replays because just picking a different tech at once stage could have a massive impact on how the race played, without creating a bottleneck or choke point because the next tech requires you to have researched sufficiently in a different branch, as is the case in many other games.
It's slightly unrealistic though. If you research kinetic weapons at level 1, why should you be able to pick Uber-Plasma-Weapon at level 8? I prefer making choices and having to deal with the consequences.
Missiles or Lasers? Damage or Range, Reload-speed or Accuracy? Balanced or specialised? A tech-tree should be a decision tree and sometimes one choice should exclude others.
I should be able to build a ship with thousands of totally inaccurate missiles that I can fire all at once. Or a ship with a hundred very accurate missiles I can fire slowly but are almost guaranteed to hit. Or a ship with maybe 500 missiles that fire with medium speed and have medium accuracy.
Now if you want all the techs, then fine, you can spend all the time researching it. But I think I'd really love to see some techs that exclude others, maybe because they make you see the universe in a certain way... which makes it inconceivable to see it the other way.
Off the top of my head, something like: you can invent hyperspace jumps, or you can have warp-drive. Not both.
E.g. Jumps are faster, but each jump has a miss-jump chance, and each jump has a maximum range, but you get a "Surprise" round because you just appear in the enemy system. Warp is slower, but no chance of going to random location. Hyper jumps have small penalty for ship size, but arrival placement is random in a target area, so there's a fleet size limit. No fleet size limit for warp, but a much larger fuel/energy penalty on hull size.
Now I'm not saying GalCiv3 should have this particular example. But I'd love it to have the concept.