High quality items will drop with more people in the party. However, the items may go to someone else. You can solve this problem by going with all henchmen, letting them die, then farm away from them.
Well of course you will only do this in area's you know you can handle, places that you can solo anyway. I dont know if it was a coincidence but I did get a couple of purples and golds better than the usual, at "the wilds" while doing it this way.