You can see Selena's recording studio, her car, her awards, her awesome outfits and other Selena memorabilia. It cost $3 and it's worth it. The family did a good job and it was touching. Of course, it's hard not to be sad when you think about someone so talented, beautiful and happy being murdered so young. It's also worth going to see the statute on Bayfront/downtown. That's a nice area to walk around anyway.
(If you visit the Selena museum, the Mexican restaurant across the street is really good)