I wish this was any other winter and I'd be going with you! Fortunately, while the Mayans may have been avauntgarde astronomers, I don't have any reason to suspect they had any real prophetic gift. I strongly suspect there will be opportunities beyond 2012 for cool trips!
My comment is in consideration of the idea of convoying into Mexico. This is a great idea... I know we wished we had a buddy vehicle along with us for that portion.. but if the convoy gets too big, say more than 2-3 cars, I think you might bottle neck a little at the border. We left AZ early morning from about 40miles north of the border. By the time we secured Mexican auto insurance, dealt with the border crossing, then stopped for our vehicle carnet/customs, changed some money, we didn't make it to our planned campsite until evening. Some of those stops were just a matter of waiting in a line one vehicle at a time so if there's 3 parties traveling together it will take 3x as long.
Do you guys know where you're crossing the border?
Have fun (jealous)!