NichG, what you mentioned about multiple playthrough carry-over actually relates to a different Roguelike concept I had a while ago, a roguelike where the dungeon warps and adapts to the player's last playthrough. For instance, if you die to spikes there might be a level that acts as an easy spikes tutorial, or if you drown you might see a water level (the game design point would be to teach, tricky to design though.)
Further, I considered having some persistent dungeon flags such as permanent changes that occur in the dungeon... you dig out a wall while playing and it unleashes an aquifer, subsequent adventurers have to unflood it. Or you crack into a new area full of lizardmen, and those enemies begin to populate the main dungeon. Etc etc. So the dungeon state changes continuously. Winning is the ultimate state-changer, causing something dramatic to happen which drastically changes your next play. Etc.
I might not use that here because that's too many original ideas and modifiers and new systems to code for a single game but it's definitely an idea I'm fond of.
EDIT: A wonderful game that basically used the aforementioned paradigm is Baroque by Sting.