One of the main reasons to play a game over and over can be custom made content. There are still people building maps for RT3 and other games. Games like heroes of might and magic 3+ or starcraft I (to name totally diffent game types as well) have been tremendously successful because of their missions and maps made by the gamers themselves.
Do you have any plans or ideas to provide tools for something like this, perhaps with an addon, a sequel or something?