Place Nilla Wafers and Pumpkin Pie Spice in a food processor and process until only fine crumbs remain. Remove two tablespoons of the crust mixture and set aside for now.
Carefully pour the melted butter into the food processor and pulse a few times to combine the butter with the crumbs. You want the butter to be evenly distributed.
Press the crust mixture evenly into the bottom of a 9 inch springform pan. Cover the crust well and place in the freezer to set up.
Cream together the cream cheese and dark brown sugar in the bowl of a stand mixer or a large bowl with a hand mixer, until light and fluffy, about 4 to 5 minutes.
Mix in the pumpkin puree, vanilla extract, and pumpkin pie spice until smooth and thoroughly combined, about 2 to 3 minutes. Make sure to scrape the sides and bottom of the mixing bowl as needed.
Gently fold in 3 cups of the whipped topping until fully incorporated.
Transfer the cheesecake filling to the springform and use an offset spatula to smooth the top.
Cover and chill the cheesecake overnight or for a minimum of 6 hours.
When you are ready to serve, spread or pipe the remaining whipped topping onto the top of the cheesecake and sprinkle on the reserved crumb mixture and pumpkin pie spice if desired.
To serve, remove the springform rim, cut and serve. Drizzle with caramel sauce if desired.