I don't think so, because just like in every sport, all the umpires do it a little bit differently and are more or less disposed to calling or letting certain things go. Players that have been in their respective pro sports for ages (this applies to other sports too) become familiar with the longtime umpires and are aware of what kind of tendencies this or that umpire has, and how he interprets certain things. It's not like a complete change of rules but a different umpire will always bring with him a slightly different interpretation of the rules that experienced players will either exploit or be extra careful about. Even if they did know that the umpires were switching to the bench, which they obviously wouldn't, being so engrossed in the flow of the game they are playing, it would be too hard for a player to keep switching between the interpretations of the rules that different umpires have. The ball could come his way and he might get away with a little shove, then the next time it comes, the umpire could have been interchanged and he might get whistled for the same shove on the next play.
Agreed that the game is WAY faster and more demanding on the umpires, and even another umpire on the ground would bring with it the same problems I have addressed above. I don't know what the solution is, but I don't think an interchange for umpires is it.
IMHO. Good question though. I think it would make the umpiring different but not necessarily better.