Where do dungeons fit in this game SE?

[Rainsworth]

If you read my first post...or any of them you'd see I said I have no clue where to make them fit into this game, and no I don't expect them to drop BiS or anything dumb like that. The people that asked what I would like them to do don't understand my position. I'd like a reason to do them more than once. I literally have no idea what should be done with them, but saying they have a real purpose in the endgame right now is just flatout wrong. I need to go edit the initial post and throw the word endgame in there i guess to streamline the focus.

Let's pretend that you are right: how would you make them useful at lvl 50?