The Space Center is definitely worth the price! Great for children and families, super interesting for people who want to learn more about the history of space exploration.
If you want to see the historic Apollo Mission Control Center, make sure you have enough time during the day. You need to book a (free) ticket for the white tram line, which is high in demand apparently. I saw in the reviews that these tickets are sold out within the first hour after opening. It's not entirely true, because they release more tickets during the day. In my case, I arrived at noon and was able to book a ticket via the app at 1.30pm. Ask the staff when the new tickets are going to be released - they are very kind and made this journey unforgettable for me. The white tram line only covers the Mission Control Center, so you might need another day to try other tram lines as well. The tour was guided, but the speakers on the tram were not loud enough based on my experience. Also, make sure that you arrive in time for boarding. I had some issues with the app - if you experience the same, just talk to the guys at the service desk.
Overall, this is a must-visit in Houston for the whole family.