Something worth considering about dark ride photos.
You are chasing something that will unfortunately come down to money. You'll hear people say "the camera and lens doesn't matter, its the photographer that counts". But when it comes to dark rides, it mainly comes down to equipment. If you give a Sony A7sII and a Sony A6000 to the same photographer, the results are going to be significantly better on the A7s. Of course, there is about a $3000 price different between the two.
I'm not saying that a great photographer with a lower spec camera cannot get better dark ride images than someone who doesn't know what they re doing with high priced equipment, but given equal skills, the better gear will win.
You'll probably never be happy with your dark ride results, because you will be comparing them to what you see on line, where people have put considerable time and money into chasing the best possible results.
My advice would be to not focus on trying to master the dark rides. Get a camera that performs well for the vast majority of shooting situations - portraits, landscapes, general family scenes.
If you are getting just a single lens, make it a wide to tele zoom (something like a 24-70 on a full frame or 16-50 on a crop) . You can't beat the flexibility, and it will let you get images that you would otherwise be unable to do.