I'm relatively new to GC2 and am really loving this game. It keeps getting better with each and every patch! Everyone else is tossing out ideas for features so I'll join the chorus. These are all thoughts I've had while playing the game over the last few months. I've seen some of these mentioned in other posts, consider duplicates to be a vote for the idea

. So here goes...and thanks for listening!
Tech Trading
I'd like an option somewhere between the 'no tech trading' and the current system. I like trading for technology, but with the current system, it's far too easy (and tempting) to gain and hold the tech lead via tech trading. I'd like to suggest something along the lines of...
1) If you can currently research a tech, then you get that tech in the trade. You're engineers understand the tech well enough to put it to immediate use.
2) If you trade for a tech is higher in the tree, the trade only reduces the time to research every tech between the one you can research and the one you traded for. In this case, you're engineers have to dismantle the tech and gain some knowledge from it but end up with a bunch of expensive paperweights. You can't actually put the tech to use without more research.
3) If you want the current tech and the higher tech, you can trade for both for a higher price. You get the current level tech and the time to research is reduced for the other(s).
4) Every time you trade for that higher tech, it reduces that time/cost some more down to some minimum number of weeks, but you still have to research the tech to get it or continue to trade for the current level tech to trade up to it.
5) I suggest the AI refuse to trade the higher tech with you more than once per turn..."What!? You broke it? You need to learn to take care of the toys we give you before we'll give you more. Come back later!" However, you could go to another race and make a trade that turn.
6) Effects of trading for multiple techs within a branch would be based on the highest tech traded for. Effects of trading higher techs in different branches of the same tree would be cumulative for 'trunk' level techs.
7) Stealing a higher level tech would have the same effect (reduce time to research rather than just getting).
8) Possibly limit the amount of reduction in time you can achieve to 2-4 week(s) for higher difficulty settings and allow the player to reduce the time to 0 weeks for easier difficulty settings.
9) The reduction in 'time to research' could be based on difficulty setting so on the easiest setting, tech trading works as it does now. For higher difficulty settings, the reduction could be set to minimal so tech trading gets extremely expensive.
For example, I'm able to research Lasers; the Alterians have researched through Laser V. If I trade for Lasers, I get Lasers. If I trade for Lasers V, the time to research Lasers I-V is reduced by 25% (or some other amount based on difficulty setting) and I still have to research Lasers I. I can trade for Lasers and Lasers V for a higher price to get Lasers and reduce the time to research Lasers II-V. On the next turn, I can trade for Lasers V again and the time to research Lasers II-V are reduced again, etc.
This would make tech trading techs and multiple techs much more expensive and slower for the player. Based what I've observed of the AI's tech trading abilities, I think the AI could be left as it is and use this system to balance the player vs. AI in tech trading.
Fleet/Ship commands
I'd like to have the option of commanding my ships/fleets to 'patrol' 3-5 sectors along my borders. Similar to the 'sentry' command except ships would move 1-3 sectors to either side or in a 2-3 sector radius circle around the position I give them the command. If an enemy ship is detected, they'd stop and await orders, maybe with a 'Battle stations' popup.
New Ship...station barge
I'd like to be able to build a ship that could be attached to a space station and tow it to a new location. It would require one of the larger hulls; have the same speed as a constructor unattached but a much much much slower speed when attached to a station. The attached speed would be a function of number of installed modules (~4 weeks/turns per sector for a initial station and add a week for each additional modules). It would be intended for moving influence, military and economic stations. I suppose if you want to tow your mining station off its resource, the player should be allowed to do that, though IMO that should result in the destruction of the station and the ship. Or for fun, let it be used offensively to pull an opponent’s mining station off their resource, resulting in a war of course, if you're not already at war.
Planetary Invasion
I'd like to see this expanded into a mini-game. Something similar to sacking a town in Pirates! only with a bit (actually a lot) more depth to it. Selecting the 'normal invasion', planetary bombardment, etc. invasion options would affect the terrain and troop types required. Perhaps allow you to select the troops and type of equipment that are loaded on the transports or set the percentage of each troop type when the transport is loaded. This would probably require adding a few more techs to support this to give the player more options as far as troop types and assault equipment. The current system is fun to watch the first few games, but after that, I always skip to the end. This is probably something for GCXXV, but I'll wait!
Resource Mining
Instead of having the various resources floating around in space, make uninhabitable planets hold the resources. You send a constructor to a 0 PQ planet and attempt establish a mine on it and have a chance of discovering one of the existing resources. If the planet doesn't have a resource, the player can leave the mine there for some small influence effect, upgrade it to one of the other station types. Or dismantle it and allow the constructor to move to another 0 PQ planet to try again. Perhaps late in the game, a random event occurs where an old mine discovers a new vein of a resource or a productive mine is exhausted.