I love the Barber museum, I've been twice now. The racetrack is also fantastic, I dream of tracking my M3 there some day.
If you're in TX, I'm guessing you're headed toward San Antonio and Austin. I have heard there are great roads in the hills West of Austin but I can not personally vouch for this. Night life in Austin is supposed to be fantastic with live music everywhere. Other points of interest if you're headed toward DFW might be the only North American RUF dealership. Again, I haven't been but heard it would be worth it to stop by.
If you find yourself in Amarillo, you can grab a steak, waste some time, and mark it off your bucket list at the Big Texan restaurant. <-- 72 oz steak dinner if you dare. Carhenge is also just west of Amarillo. It's a spot to get off and stretch the legs but not much to see other than back halves of 60's boats sticking out of a cornfield covered in 6" of spray paint. I think a drive through Palo Duro Canyon, which is just South East of Amarillo, would provide some excellent photo backdrops of the 2nd biggest canyon in the US.
BTW, great RR. Excited to read about your next update.