How much are you willing to forgive edits required if you really like a manuscript? I think people have the idea in their mind an editor will only accept something if it is absolutely perfect, but if this is really the case, then how come there is so much editing done after acceptance?
If I really, really love an idea, I'll work with the author to try to bring that idea out. I've been known to have people do three or four major rewrites and then still do polishing even after that. When I have the time (so not right now), I like to work with people on their manuscripts. However, that being said, I don't actually acquire a manuscript until it has been rewritten into a fairly workable state. It may still need line editing, and it will definitely be copy-edited, but the manuscript's bones are now there. I don't acquire until then because I don't want to buy a manuscript and discover the author can't rewrite. Nothing is more frustrating then that.