Thank you. Smarter than what?
Turning the demographics is not the only thing the Mexican government would have to turn. They have a country they can't run as it is. Making it bigger won't change that. The resources of the area will not in and of themselves determine prosperity.
Besides, secession has already been tried once in the US. It didn't work then and it won't work now.
A wall is a wall is a wall. How much will we have to pay our military people to make it worth their while to gun down unarmed immigrants from atop the Great Wall of America?