It's about 80 miles from Austin, or 20 minutes the way y'all drive.
New Braunfels and Guadalupe River is LOTS of fun in the summer for a slow, lazy float.
Hill Country isn't far - and beautiful!
Downsides: Heat, humidity. Kinda like Florida, but without an ocean view. I'd take it over DFW any day. Having lived in DFW and been back there a year or so ago, it is REALLY exploded and gotten even busier.
I'd take SA or Austin/Hill Country any day.