I found that Wallch worked fine in Cinnamon on Mint 12 - provided you started it manually. Trying to get it to start automatically was not at all successful.
If you install it from the Software Centre on Cinnamon Mint 13 actually seems to work on start up.
It looks to me as if somebody's worked on it to make it compatible with Cinnamon. It's not perfect - it won't appear in the system tray unless you start it manually, so it's not so easy to get at the preferences, but once you've got it set up, hopefully you won't need to change them often.