We did it last October and I'm glad we did. I think it is worth doing once. Previous posters say they wouldn't do it because they used to be able to watch the fireworks from the terrace for free. But since that's no longer an option, you have to look at what you can do in today's world.
1) Grab a Dole Whip or something from the Main Street Bakery, position yourself at least an hour in advance to get a good spot for viewing, stand or sit on an uncomfortable sidewalk for that time, get annoyed by all of the people jostling you and around you, get really annoyed at that person who figured it was OK to get right in front of you , etc. or
2) Pay an overpriced sum to get all you can eat desserts, a seat, an uncrowded viewing area, great location to see Tinkerbell and the fireworks, and a PhotoPass photographer that can take a pic of you and family with castle in the background and no other strangers in the pic at all. or
3) Chuck it all and grab a nice sundae at Beaches and Cream!
I've done option 1 and really hated it. I've now done option 2 and enjoyed it, and will probably now opt for option 3!