I LOVE that idea sounds totally cool and I would love to see how maxis would do it!!! Plus think of all the goodies we could find there *rubs hands together* something like a tim burton film! xD I would LOVE that!
About the scary creatures thing, that would be a good expansion pack for people who want different creatures back into the game (vampire, werewolves) unless they go for something different and unique like creating their own monsters.
But that idea sounds so awesome! ^_^