I'd suggest two changes:
1. Let players get experienced based on their current level as opposed to the level of the dungeon they are running.
2. Give experience and end game currency bonuses for helping lower level players get through dungeons that are at or near the low level player's current level.

So if a level 60 player helps a level 15 player run Satasha, he'd get law and esoteric tomestones like he was running an end game dungeon. I feel this change is necessary because the current system creates a conflict of interests between helping your friends and farming currency. These changes would help alleviate the problem.