I received a response from the Texas State Parks Region 3 (Central Texas) Director Todd McClanahan.
Rather than paraphrase, I'll just post the pertinent sections of the email.
"Since this is a relatively new policy for Texas State Parks, we too are trying to adjust and keep up with the demands of this growing and popular activity. Currently there are not any parks within my region (central Texas) which have designated an area for unmanned aircraft (drones). I have however asked the superintendents to give it some consideration and evaluate their sites individually to determine if there are any feasible locations where this activity might be safely conducted.".
He also went on to say :
"I personally followed up with the Superintendent at Inks Lake, along with all other park superintendents, to ensure their staff are aware of the policy and that it’s not just a purely prohibited activity and to understand some of the background information as well."
And finally:
"Again, I appreciate your patience as we continue to evaluate the possibility of allowing unmanned aircraft in some select state parks. I’d be happy to follow up with you if there are any parks in central Texas which find a suitable location to allow this activity."
Personally I think this is a very encouraging response. I responded, thanking him and offered to put together a short informal presentation and demonstration for his staff, so that they can make a better informed opinion. I'm new to the UAV hobby, so I will be coming here for input if he takes me up on that.