Well as far as asteroids fields i wouldn't eant to see them gone. I would want to see a more realistic circle around a solar system where planets can be on either side or ehere there are teo in a solar system. As far as manuverability. Not an issuebyhey are a few million kilometers apart,  but this may depend on how old the solar system is.

Now as far as starbases are concerned some games like shattered suns and sins of a solar empire use starbases as there main mechanic other games. What i would like to see is an option to go either way where you can dominate by planets,  starbases,  or inbetween. Most importantly they need to look nice,  snd ai's need to be able to use them right.

Asteroid mining will be in the game. It will be done with starbases and add production to a nearby planet much like GC2.

As for starbases being underpowered, you must not really be using economy starbases. They are awesome. That said. I never build military or influence starbases as I find the influence ones to be pretty ineffective and I am almost always the aggressor in war and find the stationary nature of military starbases too limiting.

Economic starbases are incredibly powerful.  Kind of rediculously powerful, since you can stack the effects of several starbases on one world.  I am actually hoping they "nerf" that a bit before release, so that maybe a planet can only receive bonuses from 1 starbase.  And now they are even better than they were in GC2 in one major way; you can have a fleet stationed with the starbase to defend it.

You should try them out sometime.  You are really kind of gimping yourself if you are not using them.