If you are in the area, I'd be interested to hear about Balmorhea State Park. There's supposed to be a big natural pool there (similar to Barton Springs, but bigger), where the water is about the same temp year-round. They have cabins if you want to stay there too.
It is kind of close to where the I-10 and I-20 meet.

Let me know if you make it further east. I'll be doing a swim event in the Highland Lakes, just west of the Austin area, in a few weeks. One day at Lake LBJ, the next at Inks, and the last at Lake Buchanan.

Not sure if UA still flies to SJT? I think AA does, and I' flew there on CO (IAH-SJT) ages ago. Might be worth comparing costs, but the town isn't anything more than MAF. If you're into steak, there are some good steakhouses in San Angelo.

Otherwise, I've only driven through this area, but have been wanting to visit Big Bend and Marfa for some time... Definitely post a trip report and a link to it from here.