Starbases can be essentail, but they also are far to powerful. A fully whacked up military base in the right place is just far to powerfull, all the advantages it gives to nearby fleets mean they are praticaly indestrutible. This is so cheesiy its painfull, esp as the AI doesn't seem to really use them allowing me to dominate if I so desire.
I would suggest toning down star bases a bit and make the AI better at using them, rather than just building 30-40 infulence bases on my borders and not upgrading them how about it making them prioritise upgrading a few strategic bases.