I would like to preface this by saying that I have only done a couple of the Lv.50 dungeons. In all cases it was a bad experience, some of it was the people I was grouped with, but I think the larger issue is that the dungeons and their incentives are poorly designed.

Boss are the only ones that give Tomestones, and are the ones that reward you with coffers that give the most desirable equipment. So every party I've gotten into has the tank pull the entire leg of the dungeon with the rest of the party following close behind. When they reach the boss the tank dies in a corner and the healer raises them after the enemies have left the area. To my knowledge there is no incentive to do battle with the enemies that come before a boss. In fact, because of the way that armor degrades, you will save quite a bit of money by avoid encounters even if you die a few times along the way.