Beat the cream cheese, pumpkin, 1/4 tsp. pumpkin pie spice, and sugar together with a mixer until it's well blended. Gently fold in the Cool Whip until everything is combined. Spoon into cooled shells and refrigerate until firm. (Or, fill a plastic sandwich bag with filling about 2/3 of the way, push into one corner, then snip the corner of the bag. Pipe the filling into the shells--it's super easy, and you can throw the bag away!) Serve with a dollop of whipped cream (I like to beat heavy cream and add a little powdered sugar, or use spray whipped cream) and a sprinkle of cinnamon or pumpkin pie spice.