I agree JoeMud, the external sounds would add greatly to the game. Being able to hear that nme plane as he booms over my cockpit would be a thrill, specially if i could hear his cannons going off (and missing hehe)
In the game "Fighter Ace" I have been able to hear the engine settings of a target while in a dogfight, it is a nice clue to hear that guy Throttle all the way back trying to force an overshoot, I can use all the cues I can get in AirCombat

plus wouldnt it be cool to hear the bombs exploding around the base as you stand in the tower, rather than just the quick explosion graphics we have now?