Your 18-55 will do the trick for most of what you want. I have contemplated purchasing a better lens with longer reach (e.g. 18-105). If I had that, I would never consider taking anything else.
I used my 50mm 1.4 at the Aladdin show and some of the shots turned out great. No way I could have done that with my 18-55. You will like having your 35mm 1.8 around.
I have a Canon t2i. I have brought my 55-250 kit lens a couple of times and aside from looking for a shot where I could really use it, I really didn't need it.
If you don't already have one, I recommend a lowepro topsider or something similar. My camera and kit lens drop right down into the case to keep the camera protected while on rides and in lines. Still accessible enough to grab for some pictures if I want, but most of the time I'm enjoying the ride. Also nice is the waterproof slip cover for rides like Splash and GRR. You still need to be careful as the cover doesn't provide 100% coverage, but it's close.
I remember this. No picture is any good if you don't have your camera ready to take it. I end up using my cell phone camera a lot because it is right there. The pictures are never as good as my dSLR, but they are more than passable for capturing the moment and the memories. Point being, take the most convenient lens (18-55 in your case) and don't worry about the picture quality so much. These aren't going on the cover of sports illustrated. Get the shot, move on, and enjoy the parks!