Heat oven to 250º F. Combine the popcorn, pecans, almonds, pumpkin seeds, chili powder, and cinnamon on 1 or 2 large baking sheets and place in the oven to warm through. Meanwhile, combine the sugar, corn syrup, and butter in a medium saucepan and heat to boiling. Without stirring, cook over medium-high heat about 10 minutes or until the syrup turns a rich brown and a few drops of it form stiff threads in a cup of cold water. Stir in the vanilla.
Remove baking sheet from oven and pour the syrup over the popcorn. Toss quickly with a spoon. Cool and break into pieces.