I am encountering the same thing right now on my dual-boxing team (warrior and priest). I was loving the RAF bonus all the way to 60 and once that was over it was certainly painful. My advice to you is to stick with it because when you hit 70 it will all have been worth it in the end.

As others have suggested, stay away from collection quests (e.g.: the purified hellboar meat quest, the eel filet quest, etc) that have notoriously bad droprates. Collecting items off the ground can be annoying with multiple characters, but it is easy xp....