There needs to be a way to destroy old buildings if we don't want them anymore. I'd like to be able to bulldoze an entire urban district to make way for a wonder or just to clear up the urban sprawl. Sometimes the places where those buildings were put don't make much sense in being there anymore, especially if the resources next to them suddenly vanish between ages.
History may be built in layers, but not everything lasts to be built upon. Sometimes things just decay, what once was a populated district could be abandoned and left to return back to the Earth in which it was built upon. This is a fact of reality and should be possible in the game too!