So I just played against my son and totally wrecked the game. It seemed way too easy because the Starbase was cheap, had plenty of upgrade slots and had a power module outside of the upgrade tiles that always remained there.
I saw that and upgraded all my Starbases with drives and some nice cannons, built all four of them and them proceeded to wreck everything in my path.
Then I googled for a quick question on where Starbases fall in terms of "largest ship" size for when an alien ship hits... Then I was led here and found out I was totally cheating the entire time and that you can't equip them with drives to move them around.
I looked through the rules and it seemed like the instructions just sort of mention it briefly in one spot, but doesn't really drive the point home.
Thought I'd figured the game out. Only to find out that I just screwed the game up. Oh well! Next time I'll know. They sure did feel really overpowered and unbalanced!