I like what has been suggested so far. I think some ghostly wafty mobs and Indiana Jones like underground structures and auto-generated redstone traps and secret doors would be bang-up. The idea that mobs aggro in response to damage to the dimension is cool too. A scary-ass minotaur that randomly wandered the area would be cool too. I also think a type of villager-like mob could wander around making minor repairs to the structures based on the original seed and prefab structure blueprints. Perhaps trading in ores, or perhaps not having the trading aspect at all but just resembling a villager.
I like the canals and many of the other ideas placed into this dimension. I give it full support. However if a mod has been developed to facilitate this since it was originally posted, I don't know how interested Mojang would be in reinventing the wheel. I would like to see it in Vanilla though.