The National Park and State Park really should be their own trip separate from Marfa. It takes to long to get down there and you need as much time as you can get to enjoy them. They are both fantastic, you don't want to short change them.
The time I had R Taco it was very meh. I feel like Taco Heads was much better when I was hitting it up late night behind the bar. Now that it is an actual place to go I find it underwhelming.