What about having an offering on the Unity store?
Specifically, aspects of CW 3 or 4 released as tools for programmers.
Not the whole game's source, but rather something like the terrain-handling and creation tool.
(Anything like the creeper-handling itself might be core IP, very specific to CW, so I can understand not releasing that, though it seems that KC doesn't go back to reuse the code of an old game in a major way.)
So it might be a way to get more income out of the old games by selling parts like the terrain handling, or CW 3 scripting, used in those games.
I was always impressed by the different terrain systems of CW3 and CW4.