Pull the one good thing(concept) from abyssea for the sake of scaling diffuculty. Make it increase/decrease mob and boss levels based on the speed your running through the raid, also scale drops based on the difficulty rating you achieve. The faster you run the harder it gets but the better(more likely) your rewards.
In a mass currency farming system this would affect the amount dropped/person at the completion of the raid, for single item(mythril and what have you) it would affect rates scaling from ~1%@max time up to ~99%@20minute run, as a for instance. To take it just a little further it could be a token+ system where you get your currency(totem w/e) x1 everytime but you get a [i]chance[/] based on how high you got the dungeons diffuculty rating to get a second/third/fourth/etc.
