Haven't done one at DCA. osh has so he'll be your best information source because he did the World of Color dessert party a couple of years ago.. We did the World of Color dinner package, ate dinner at Carthy Circle and received a pass that specified a time and section from which to watch the show .
We have done dessert parties at WDW.
At Magic Kingdom there is an area with tables and then a dessert/ snacks buffet near by. At DHS you enjoy desserts and snacks in the Animation building for the Star Wars Fireworks and then are escorted by storm troopers to an area in front of the Chinese Theatre to view the fireworks.
Each dessert buffet seems to have an ice cream station, cookies, many tiny desserts, treats and a variety of beverages. Lately they have added cheese and crackers!