To find symmetrical dwarf shrub suggestions, the first place to go to find a list of potential plants is our Native Plant Database. Use the Combination Search feature instead of Recommended Species. This will provide a bigger selection with much more choice to narrow down. The volunteers and staff at the Wildflower Center who maintain the database have partners in different regions to help with these recommended species lists based on what is easy to access in local nurseries.
Under Combination Search, select the following categories: Texas, Habit/Shrub, Duration/Perennial, Size 0-1 ft or 1-3 ft. You can narrow down this search further by indicating your specific soil moisture and light requirements. All native plants will bloom to some extent. So here are some shrubs that will grow to around 3 feet that have less showy blooms;
Symphoricarpos orbiculatus (coralberry) (it does have showy purple fruit though)
Acacia angustissima (prairie acacia)
Dalea bicolor var. argyrea (silver prairie clover)
Ephedra antisyphilitica (morman tea)
Hypericum prolificum (shrubby St. johnswort)
Leucophyllum candidum (purple ceniza)
Mahonia repens (creeping barberry)
Prunus minutiflora (dwarf plum)
Paxistima myrsinites (myrtle boxwood)
Quercus havardii (havard oak)
Follow each plant link to our webpage for that plant to learn its growing conditions, bloom time, etc. At the bottom of each plant webpage, under Additional Resources, there is a link to the USDA webpage for that plant. Take a look there for more specific details about suitability before you put them on your final planting list. Think about including plants that have interest during a variety of seasons and that have more than one attractive feature (fruit, foliage, bark, etc.) so you can get more benefits out of fewer plants.
About agaves and century plants, follow this link for a Mr. Smarty Plants answer to your question. They flower after 8-40 years (depending on the plant vigor) and then send out several baby offshoots that can be transplanted to other locations. The main mother plant does die after it flowers.