Heat oven to 350 degrees F. Grease and flour 2 (9-inch) round baking pans. Beat cake mix, 1 cup pumpkin, milk, oil, eggs and 1 teaspoon spice in large bowl with mixer until well blended. Pour into prepared pans.
Bake 28 to 30 min. or until toothpick inserted in centres comes out clean. Cool in pans 10 min. Remove from pans to wire racks; cool completely. Beat cream cheese in small bowl with mixer until creamy. Add sugar, remaining pumpkin and spice; mix well. Gently stir in Cool Whip.
Cut each cake layer horizontally in half with serrated knife; stack on serving plate, spreading cream cheese filling between layers. (Do not frost top layer.) Drizzle with caramel topping just before serving; sprinkle with nuts. Refrigerate leftovers.