[AgentZero]

The SE3 ship purchase menu. That window was a lot simpler way of quickly getting planets and spaceyards quickly working on building a new fleet with significantly less menu-clicking as in SE4. Perhaps a few refinements as well, such filters to select the system, and only planets and/or shipyards.

Also, I'm in favour of bringing back SE3s Repair/Build Queue window, and also the ability for Bases to have more than one Space Yard comp on them. The main reason I'd like to see this is so that ship hulls can have the requirement 'Can Only be Built By Base with X number of SYs'. A tech that decreases the size of SYs would also make this interesting since you'd have the choice of researching bigger bases or smaller SYs (to fit more into an exisiting base) in order to build your big new Battle Cruisers.

Also, I'd like to see techs that once researched provide immediate bonuses in certain areas. So research in one area might uncover some new mining technique that could be applied to existing mines without needing to refit them, so all your mines get produce 10% more minerals. Or advanced targeting algorithms that give all your ships 5% accuracy bonus. This would allow players to make small, evolutionary improvements to their empire without having to take the time and expense to upgrade everything.