Preheat oven to 250°F. Place popped popcorn in a large bowl.
In a medium saucepan over medium heat, melt butter. Stir in brown sugar, Cheerwine syrup, and salt. Bring to a boil, stirring constantly. Boil without stirring for 4 minutes. Remove from heat and stir in baking soda and vanilla. Pour mixture in a thin stream over popcorn, stirring to coat.
Place in two large shallow baking dishes and bake in the preheated oven, stirring every 15 minutes, for half an hour. Remove from oven and let cool completely before breaking into pieces.