I have a suggestion Maybe make the upgrades cheaper for the first initial 2 on the starbase, and have it get more expensive the more upgrade's you add on. Oh and how about being able to use all the upgrade's for the starbabes instead of only getting 7. I mean whats the use of having them when they can't even fend off a fleet of ships.
1. Fisrt two upgrades you use on the starbase maybe costs 800/100/100
2. Third upgrade jumps to 1000/150/150
3. Fourth upgrade goes too 2500/200/200 and so fourth until your starbase has used all of its upgrades that you researched.
Also I know this maybe impossible to do now but maybe show the growth of the starbases as you upgrade them, you know have it get bigger the more health you add to it. Hanger bays be shown when added, the construction yard actually be construted around the base. Show the different types of weapons that you upgrade. Oh heres and idea to make them more usefull have them be able to be built in the phase lanes so when an enemy fleet jumps and runs into the base they are pulled out of the jump and are forced to have to engage the base rather than just fly around it. But make it so if you do build one in a phase lane you can't built one in the connecting planets gravety well.