RE: Houston mexica Restaurants
As Texianjoe observed, Taco Cabana is a fast food chain; good for a chain, but portions are pretty small for what you pay. Portions at Pappasitos are huge and I think you'll be very pleased with the food.
Spanish Flowers on N. Main @ Airline is a favorite of Houston's Finest and I don't think I've ever driven by there and not seen several patrol cars in the parking lot. It's open 24 hours, 6 days a week, but you don't need to go that far to get good Mexican.
Also, just down from you where S. Main and US 90A (Old Spanish Trail) merge, Capt. Benny's for oysters on the half shell, cold boiled or fried shrimp, catfish (get the whole butterflied cat), gumbo, crawfish etoufee, crawfish piroque, etc. Excellent stuff and a lot less than you paid at Willie G's. Also, Pappadeaux on the S. Loop next to Pappasito's.