Problem is, there really is no such lens. If there was, then we wouldn't need interchangeable lenses, everyone would just get that 1 magic lens.
Fireworks -- you can shoot with any lens, but the focal length will determine your composition. Want super wide angle landscapes, or more tightly cropped?
Dark rides -- require a fast aperture. Generally speaking, a prime lens, like a 35/1.8.
Most "all in one" lenses are the superzooms, like your 18-200. But you suggested it is too heavy.
A regular kit lens, 18-55, will cover most of your needs. Something like the Tamron 17-50/2.8 would cover the same range, give you a little more dark ride capability, and generally provide slightly sharper shots. But with either lens, you will miss telephoto opportunities. Though at Disney, I generally pass on telephoto except at Animal Kingdom.
If you want to stick to just 1 lens, then go in with an understanding that there will be some types of shots you won't be able to take. Or, make a plan of carrying 2-3 lenses as needed, to cover all the shots that you want to take.