Place your large mixing bowl and whisk attachment in the freezer or fridge for 15 minutes, and set the cream cheese on the counter at least 1 hour ahead so it becomes completely soft. Measure out the brown sugar, pumpkin pie spice, salt, vanilla, and powdered sugar so everything is ready.
Pour the cold heavy whipping cream into the chilled bowl, add the powdered sugar and vanilla, and whip on low for 30 seconds, then medium-high for 3 to 4 minutes until stiff peaks form. Transfer to a clean bowl, cover, and refrigerate.
Beat the softened cream cheese on medium speed for about 2 minutes until creamy and completely smooth, scraping down the sides and bottom of the bowl with a spatula.
Add the brown sugar, pumpkin pie spice, salt, and vanilla to the cream cheese and beat on medium for 1 to 2 minutes until fluffy, then scrape down the bowl again.
Give the pumpkin puree a quick stir and blot any watery surface with a paper towel. Add all of the puree to the cream cheese mixture and beat on low for about 1 minute until smooth and evenly orange.
Scoop about 1 cup of the chilled whipped cream into the pumpkin base and stir gently with a spatula until mostly blended to loosen the thick base.
Add about 2 more cups of whipped cream, leaving roughly 1 cup in the fridge for topping, and fold gently with a spatula until no white streaks remain, stopping as soon as the mousse looks even.
Divide the mousse evenly among 8 dessert cups, smooth the tops with the back of a spoon, cover, and refrigerate for at least 2 hours until firm and chilled through.
Just before serving, spoon or pipe the reserved whipped cream onto each cup, add gingersnaps and candied pecans, and finish with a light dusting of cinnamon.