There is also a Fantasmic Dessert Buffet at Disneyland in California. Its about $50 a person with balcony seating during the show. I don't know of any dessert buffets in WDW but I am sure there are some!
Private dining dessert buffets are also common, such as the Illuminations Dessert buffets.
(BTW, we did the dessert buffet at DL for Fantasmic and it was so nice. Not just the desserts, but the special seating for Fantasmic. I would do it again in a heartbeat.)
One is prior to the Wishes! cruise and runs for about 45 minutes starting 1½ hours before Wishes! starts. It is near the Contemporary dock. You then board the boat and see the Electric Water Pagent real close up and then go into the Seven Seas Lagoon and anchor on the extended centerline of Main Street to view Wishes! with the music and narration piped in.
The other is with the Epcot International Dinner and you will be escorted to a private IllumiNations view area with a dessert buffet set up.