Can you elaborate? Most editors have SyncTeX (http://mactex-wiki.tug.org/wiki/index.php/SyncTeX) support and most viewers can handle that. You can pretty easily build on every change. Also, when the document becomes long, you can split it in multiple parts that only get rebuilt if they change. That's a sane way of organizing things anyways.

I never had any performance probs.

Damn, I tried your case and didn't work. I'll have to do some investigating.