Personally, I wouldn't want them. They'd just be one more thing to get hung up on, catch something on the edge of the course, etc.

Once you were on the bike and racing it wasn't cold, or at least you didn't have time to notice the cold. I only noticed my feet feeling cold once during the entire race, and that was in a 5 second break between trying not to wash out in switch-back turns. Oh, and there was a bit of "my ass just got soaked w/ frigid mud water" clenching in the first 10 seconds of the race. On the last two laps I was actually starting to get too warm and would have ditched my arm warmers had that not certainly sent me into the underbrush.