a call doesnt always mean a draw...its just a good indicator. would you raise with 78 here? only if you are afraid of the spade.
you may also slow play a set, but prolly not on this board.

however, you have nothing but potential with this flop...and BIG potential at that. therefore, why dump money in when the aggro says he hit something? he may be on a bluff, but he may have bottom pair, too. and bottom pair has you beat, but barely because of your draw. thats why you float, imo. you want to catch something you are more comfortable playing.

raising with AQo is a completely different story. you advertise power to blow him off his bluff. when he plays back, you dump w/o costing too much. because of the spades hitting the flop, you are gambooling for a stack because he is aggro.

smart aggro, or uber-aggro, makes no diff to me here. i know he will lead as long as i let him. and i can bust him if i hit.

of course, if the A or Q hits only, i lose my stack almost everytime here w/o a second thought.

but he hit a 4-outer on the river? not much you can do here, either. he got quite lucky the "right" spade hit.