Preheat oven to 325°F.
Whisk together egg whites, Worcestershire sauce, sugar, paprika, and cayenne in a large bowl.
Add popcorn, pretzels, nuts, and salt to taste and toss until thoroughly coated.
Spread evenly in 2 buttered large shallow baking pans (1 inch deep) and bake in upper and lower thirds of oven, switching position of pans halfway through baking, until coating is crisp, about 20 minutes total.
Spread mixture on 2 large sheets of parchment paper or oiled foil and cool completely.
Cooks' note:
Spiced party mix can be made 3 days ahead and kept in an airtight container at room temperature.