It's probably worth somewhere between 1 to 1-1/2 hours. There are a few planes, including a couple of Dales. A lot of the history focuses on the toys and other aviation related stuff. The facility is very nice and the docents I interacted with as well as members of the Stanzel family were very passionate about the place. If you're in the area I'd say it's a worthwhile trip.
P.S. We came from the New Braunfels / Canyon Lake area and swung thru Shiner, home to the Spoetzl Brewery and Shiner Bock beer, on the way back. I liked the museum, the rest of the group liked the beer.