Next to the pvp battleground queue there should be a "Quick Exp!" button. The arena stuff is boring and i never see anyone doing it. It could auto join you with teammates close to your level and give you an exp boost for each teammate. It could just be a little tiny zone, like 2 or 3 rooms with waves of slow walkers comming at you. But no real big bosses unless there is a way to kite them that way players dont have to worry about healer or tank to do the quick group exp farm. It could even have reduced drops like less gold and less chance of finding stuff seeing as i ts more geared to exp.
Sometimes your quests run dry and you cant find a team for your dungoens at all. This would be a fun solution i think.