Well, that would pretty much suck. It may work for simple setups, but when you are using a library with tons of articulations not to mention midi timing which fits only that particular library (anyone who loads a midi piece done on library A and plays it on library B knows what I'm talking about) is going to make it a monumentous task to create a listenable midi file. Not to mention that Simon wouldn't be able to use his cluster horns/bones anymore, they translate rather poorly to midi. But yes, a midi "bleep" piece going up against one done with an orchestral libary which sounds real is obviously going to make a difference in how people perceive a composition.