I think the boat is a great idea, IF you are planning to use it. Obviously towing will cost you in gas, so if you are going to use it then I say go for it. There is a photo on here someplace of an Expo truck that all it does is hold the boat, IE drive it right up into the truck frame. Then the boat is your living quarters on land, and can sail it.
In other words if you are going to do it, I say go for it, it sounds like a good idea. Why do you wish to sell it before you get to Mex? If you are going all the way down you could even put the truck on a ship and sail yourself across the gap. Someone above mentioned you can put on some truck tires (like F150 size) and pull that thing over a lot of terrain. It might be able to go with you.
Also I wanted to say that we used to have that same boat in blue (growing up) and I loved it. What a great platform for sailing. Not the best, perhaps, for an over-night trip, but still a lot of fun to get out and get going.
Oh and to answer someone about the big tow rig putting that into the water, nah it is not a problem at all. In fact it is actually easier to use a long truck. The steering corrections are easier to make because small corrections make less of a difference in a bigger truck like that. It would be just like using a dumptruck to haul a piece of equipment, which we did every day back in Aspen, even in the snow, and backing it up is not hard at all as long as you have a good set of mirrors on there.