Don't give up on it yet. It's generally tight inside dark rides but that doesn't mean you can't use it! I spent three days in the parks with only a 50mm f/1.8 and got plenty of nice pics. My only real suggestions is open it up all the way to f/1.8 on dark rides and stop it down when outdoors. My nifty fifty is very sharp when you stop it down. And since it is fixed focus, remember to zoom with your feet!

Expect some "unnecessary zoom" (as Wayne and Garth would say it in Wayne's World) on dark rides, but this isn't always a bad thing because you get some nice details.
Here's some pics from the last time I took the nifty fifty to
Disneyland just to give you an idea of the how the nifty fifty works out in the real world. All of these photos are unaltered, uncropped, straight-off-the-camera JPEGs. No editing of any kind. So the composition may not be perfect but the nifty fifty has lots of potential!