I agree, an expansion set of bombers would make a lot of sense: slow moving point buckets that have a lot of firepower but poor maneuverability. No immelman turns here! Equating this game to Chess, the bomber is King--doesn't matter how many ships you loose, or how many of their ships you take out, each team has one piece they need to protect at all costs. Taking it up another notch, introduce the interceptors as Queens: Double moves, but lighten up of the damage compared to the fighters.
Ah, interceptors. Now that gets interesting. See, TIE interceptors have quad laser cannons, so does it make sense to give them reduced firepower? Even if the lasers were weaker, you'd think it would average out to the same amount of damage. A-wings, however, could be even more interesting. Aren't their laser cannons supposed to be able to rotate 360 degrees in the Z-axis (vertical axis)? You can imagine the base for an A-wing having two diagonal guides indicating where it can fire and maybe you have to choose as your action whether to face your lasers backward or forward. That could get really interesting.
As far as bombers being like kings, I think that would be good for a scenario, but I wouldn't like that as a permanent skirmish rule. I think Y-wings are plenty competitive against TIE Fighters, even if the newer craft are superior. But I totally agree about less maneuverability. Having no immelmans is a good idea, and I would go further and say that no turns would be able to move it 90 degrees. All turns would have to be less than 90. Then again, even the Y-wings broke away from the 2nd death star pretty quickly when the Rebels figured out that the shield was still up in Return of the Jedi.