Last Spring I drove from San Francisco, to Cuernavaca, just south of Mexico City, and made multiple road trips to the coast from there. It was a most excellent experience.. as long as you have like $600-750 in TOLL money to spare, it's not a bad time, I found the free roads to be quite bad, disrepair and slow as molasses when you'd get behind a line of trucks..
if you have all the time in the world, just take 'em, you'll see more of Mexico, but you'll also subject yourself to more "contingencies" as I like to call them
I can't wait to go back this spring.. driving all the way to Oaxaca.. down the west coast...
I'm not familiar with the east coast/gulf route, but I can't imagine it being much worse..
Suerte!