In a food processor crush the Nilla wafers and 1 teaspoon of pumpkin pie spice until completely crumbled.
Remove 2 Tablespoons of the crumb mixture and set to the side. This will be used to top the cheesecake if desired.
Pour the melted butter into the food processor and pulse to combine with the crumbs for the crust of the cheesecake.
Press the crust mixture into a 9 inch springform pan, creating an even layer on the bottom and pressing it firmly together.
Cover well and place the crust in the freezer to set while making the cheesecake filling.
In a large mixing bowl, cream the cream cheese and dark brown sugar with a stand or hand mixer until light and fluffy, about 5 minutes.
Add in the pumpkin puree and remaining 1 teaspoon of pumpkin pie spice and mix until smooth and combined, about 2 minutes. Be sure to scrape the sides and bottom of the bowl once or twice so that everything gets mixed in.
Fold in 3 cups of whipped topping gently until incorporated.
Gently scoop the cheesecake filling into the prepared pie crust in the springform pan. Spread into an even layer.
Pipe or spread the remaining whipped topping onto the top of the cheesecake. Garnish with the remaining crumb mixture and extra pumpkin pie spice, optional.
Cover and chill for 4-6 hours or overnight.
When you are ready to serve it, remove the cover and springform rim, cut and serve chilled.