It doesn't worry me, it's just tedious.  Even if I control every planet, I can't efficiently deal with that last fleet bouncing around, since it can hit me wherever it wants.

And yes, I upgrade more-or-less once a turn.  The AI likes to swoop past my other planets and claim the production centers, but that's a problem I can deal with.

I just downloaded the demo of this game, and it's very interesting.  Unfortunately, now that I've reached High intelligence, the AI likes to create a single giant fleet and rampage through my planets.  Since they can hit me just about anywhere, I'm often left floundering around reclaiming planets until my opponent is careless enough to defend for two or three turns, or my production manages to outstrip the fleet to the point where they can't take any of my 7-8 planets.  Any advice for cutting these fleets off once the AI has nothing to lose?

But then, I suppose that's why the full version has space-time rifts.