One thing I'm considering doing is allowing player characters to challenge a "Relic Dungeon" in order to get their hands on one of the powerful relics that are listed in the quest book. I am considering treating a relic dungon much like a rumor in that you fight two floors and then enter the relic dungeon that uses the quest rules from the appropiate game, but all monsters are replaced with their appropiate level.

Of course I'ed put some restrictions on gathering relics, like making them only available at a certian phase (like Gold), and only if the player characters are heavely behind in conquest. So what do you think of the idea?

I think your players better love Descent marathons. Also, Relics heavily break the game, moreso than Gold items, so if you guys are still playing competitively, it might spoil things. The heroes will love it, though, and it's a nice way to get those poor relics some love.

Relics are pure ownage

If you put them in, prepare to get you a** handed

Im all for using all assets available (thats why I hate that the expansions never cross-use content) but relics are really to good for RtL.