There is really only a need for one hideout that you access when you go through the door/drain/toilet (with the giant "Stolen Goods Sold Here" sign painted on the entrance)...just an instance.
All these other hideouts could have been turned into dungeons/delves proving actual new playable content in the game.
Oh and while I'm at it...why not just call the new skill line "Thieve Guild" and have done with it.