I'd say level 80 Roulette is the most pointless.
By definition it can't be done for XP.
And while it gives Allegory, it gives less Allegory than queuing up for one of the 2 Expert Roulette dungeons manually.
I guess it does give (barely) the most Phantasmagoria; but there's not much use for those tomestones. Possibly for the relic. And the crafted gear upgrades; but I don't see any reason to do that for *every* class until 5.5.

If it were me, I'd go ahead and reorganize things into a 50/60 and 70/80 roulette right now; and make the 70/80 reward 50 allegory.