Day 1: Drive from Houston stopping in Ludling for BBQ for lunch around 11:30. Arrive in SA by 2pm. Checkin and then walk to San Fernando Cathedral, Spanish Governor's Palace and Market Square. Dinner at Mi Tierra or La Margarita (which has better fajita's?). Then take river cruise and possibly Tower of America if it's not too dark. Probably get dessert to save entrance fee.
Day 2: IMAX movie/Alamo, lunch at Schilo's (Tower of America if we didn't go), La Villita and maybe walk through King Williams District if kids are up for it and then have tea at Mad Hatters. Take trolley back to hotel. Dinner suggestions?
Day 3: Drive to LBJ ranch and then over to Fredericksburg for lunch. Return via Comfort and Boerne. Will it be wildflower season? If so, where is the best place to see the wildflowers in this area? Suggestions for a German lunch somewhere? Thinking dinner at Rosario's or Sea Island Shrimp house or?
Day 4: Drive to the 4 missions (spending time at San Jose and probably just quickly seeing the others) and the Espanda Aqueduct before driving back to Houston. Lunch at Guenther House.