Hi Joel,
I love the nighttime fireworks spectaculars at Walt Disney World! I am of the opinion that the best place to see these shows from is from inside of the theme parks. In Epcot, my favorite place to view
IllumiNations: Reflections of Earth from is the bridge between the England and France pavilions in World Showcase. This has the additional benefit of having nearby access to the International Gateway for a quick exit after the show. I enjoy watching
Wishes Nighttime Spectacular from Main Street, U.S.A. in Magic Kingdom Park. I try to watch from between Casey's Corner and Cinderella Castle, but not too close to Cinderella Castle, or I lose the panoramic view.
It sounds to me like you are looking for places from outside of the theme parks to view these shows. For Wishes Nighttime Spectacular, you have a few options. As you mentioned, the boat dock at Disney's Grand Floridian Resort & Spa provide a nice view of the fireworks. You could also make a reservation at Narcoossee's, which is quite nearby, and offers a porch for watching the fireworks. The beach at Disney's Polynesian Resort can also be a nice place from which to watch the fireworks; however, this resort is having some renovations done, so you would need to check on the state of these renovations closer to your vacation to see if this is an option. I find that it is difficult to get a good view of Illuminations: Reflections of Earth from outside of Epcot. You can see some of the higher fireworks from Disney's BoardWalk, however, it is quite hard to view the whole show from outside of Epcot.
I hope that these thoughts are helpful for you, Joel. Please do not hesitate to ask if you have any further questions!