I wanted to go ahead and put my two cents worth in here, too! We usually stay at Poly conceirge / lagoon view. That gives us the perfect view right from our room and we can see the beach from the room also. Usually the beach area isn't very crowded for the water parade or for the fireworks. Like one other poster mentioned, this has got to be the most awesome viewing area. It's a straight view to the castle.
In my opinion if you were to go to watch the fireworks, and quietly went about your business, no one would even know. I don't think anyone would bother you unless, of course, you were doing something that would call attention to your group. I'd say go for it. The worst thing that can happen is someone may tell you it's for resort guests only and may ask you to leave...but I highly doubt if that would be the case!