We didn't do the grand gatherings ones but did do the premium Wishes Cruise. It was okay. Unfortunately, the speaker system on our boat kept going in and out. When I returned to the dock they credited us the $50 difference.
The view, though, is spectacular and the fireworks are lovely. That said, you can sit on the beach at the Polynesian and get the music as well as see the fireworks.
As far as the boat goes, they take you on a cruise around the lake prior to the fireworks. They provide different drinks and chip/pretzels, etc. If it is cold they give you blankets. If you like the idea of being on the water at night to watch the fireworks then this is perfect. I agree that if you are going to do it you should pay the extra $50 for the music... it is worth it. Also, remember that a tip for the driver is not included in the price of the boat. Since we typically tip 30% this adds another $50 to the cost.
We did it once but probably won't do it again. The Polynesian beach is perfect ... and the crowds are typically minimal.