They're wonderful things, military starbases. One of my games when I was being crushed as I had a large empire, too many planets, too little population, and not enough money, I though I was going down. I built a HUGE network of overlapping military starbases (cost a lot, but nowhere near as much as a single warship), and won the game because even my mediocre outdated ships were more powerful than anything the AI could toss at me. It bought me enough time for my population to recover, money to start flowing in, and I wiped out the galaxy. Good times.