I have a crazy idea. Don't know if it can work at all:
How about using this dungeon to let people experiment with being another class? I mean, letting people decide which class they want to be in that dungeon, and give them temporary stats that will be like being that class on the same level as they are. Also, let them rearange their skill points according to that class just for use in those dungeons. that way a healer, for example, can see what it's like to be a tank, and vice versa, without having to build new characters from scratch and bringing them to high levels.
Of course there should be something to allow people to get different weapons that fit their new class. This can be tricky, I know.
What do you think?