I would stick with the 8-hour layover at iah and hang out at UC or lounge for whichever airline is taking you to SCL. Isn't there a spa or mall with both Texas BBQ and Texas vegetarian to eat? Surely as you've already flown to Memphis for BBQ, you'll want to have Texas BBQ as well!

if the connection flights have any screw-up, you run the risk of missing that sole iah-scl flight as well.

Usually you're the one who answers these kinds of queries! I still love your mantra of how to get that Upgraded seat: just buy the fare :-). (And yes that's what I do for sfo/ord)