My favorite spot for Wishes! is right by the Roy and Minnie bench. It's slightly higher than the street so you have less chance of having a bunch of big fat heads blocking the castle. Here is the view:
As you can see, you can crop out the heads if you want and still have the whole castle in the frame. I left them in just because I felt it added context to the scene IMO. I also like that you get the Emporium and Confectionary in the frame since they leave those lights on for the show.
Cheers