If your can stick it out, the parks clear out at night when it gets cold. We were in WDW for the past three years the week between Christmas nad New Years. It was cold (high 20's, low 30's). We found that everyone was leaving the parks at night, so we stayed and got to do everything we couldn't do during the day. Just duck in and out of the shops for some warmth. Personally, I think the cold nights added to the Christmas atmosphere.
John