Texas is enormous. If they switched to their own currency it'd be doing fine. This "clout" and "superpower" nonsense was talked up big time by Remainers in the UK too. Guess what - post leaving nothing is observably different. The average voter doesn't care about the sort of stuff thinktanks care about. Their concerns are local. A Republic of Texas probably wouldn't have invaded Iraq, and thus may in some sense be less superpowery than the USA, but does the average Texan see that as a problem or a benefit?