Probably not. Theres a lot of improvement to do, but zoos are always on a budget. Though I don't know the financial state of this zoo, I'd expect building more structures would be a lot easier and less expensive than having to dig up all that cement. Could be wrong though
Gladys Porter Zoo opened in 1971 and having toured the facility in the summer of 2010 I would estimate that at least 80% of the zoo's enclosures (including the 1973 Herpetarium) were all built in the 1970's. This zoo is perhaps the most stagnant in the United States, with very few new exhibits during the past 30 years. Zoo enthusiasts visit because of the amazing diversity of rare species to be found there.