After totally bombing out of GC2 and suffering severe corruption of the game (see: https://www.galciv2.com/Forums.aspx?ForumID=274&AID=85471 ) I decided to try an uninstall/install to see if that would get me running again. This was with SDC, which brought up an option to delete all associated files including skins and saved games, which I checked.

But, it did not delete the games saved by GC2. (I suspect this is because GC2 saves its games in a user document directory and that support for this has not yet reached SDC or the directory list for GC2. I deleted them manually.)