I think I have just resolved this issue. It got to the point where I couldn't even start a game without it crashing during the first turn no matter what I did. So I deleted the "local content" and re-installed the game. I now wish I had run the "verify integrity of game cache" option of Steam first, but I didn't think of it in time.
Anyway, I am now able to play a few turns with any faction while using the game console, and am proceeding with seeing just how far I can go without it crashing.
NOTE to Devs: I think it would be a good idea if one of the steps in teh "GalCiv III Support FAQ" was to run the "verify inegrity of game cache" option of Steam when having issues with the game.