Considering how hard it is to put together any random group that is willing to wait through dialogue and such for dungeon quests, it's basically impossible to experience these stories, and once you've gone through them once, you lose the option to go back and listen to the story if you do manage to put together a group that actually wants to hear it.
I would propose, then, that dungeon quests become replayable but without providing any rewards after the first time. This way, there's no balance issue to consider, but you still have the possibility of some day actually hearing the story that goes along with the dungeon.
Fedrals: PC / NA / EP / NB