The MF helps, and Master 1 gives you the biggest boost. The main reason to go Master 1-2 though is a) Paragon leveling is a bit faster and b) Warden/Organ drops. The drop rate is almost non existent below Master 1 (I did get two keys on Easy though, so they do drop). I can't really say if it's the same for a Demon Hunter, but on my Wizard I just treated each Master level with DPS breakpoints. Basically, each level equals a 100k DPS increase needed to farm efficiently, starting at 100k with Master 1. I can do Master 5 on my almost 400k Wizard, but it's not worth it compared to Master 4 and I doubt it will ever be. I can't even do the Ubers solo without switching my spec either, and I have to put it on Master 3 or I get one-shot again and again vs Rakanoth.
Oh and yeah, as Daravon mentioned; mob density. It's pretty sparse at times even with that boost, and it's downright anemic without it.