In a medium saucepan, combine spice and pudding mix and cook as directed, substituting half-and-half for liquid. Remove mixture from heat and stir in pumpkin. Cover surface with plastic wrap and let stand for about 1 1/2 hours, until nearly room temperature.
Stir gently when cool. Whip cream. Fold gingersnaps and whipped cream into pudding mixture. Spread half of pecans in bottom of crust. Pour pudding mixture over nuts and chill pie for 4 hours. Sprinkle with remaining pecans and garnish with gingersnap crumbs and whipped cream.
Graham Cracker Pie Crust:
Stir together crust ingredients and press onto bottom and 1-inch up side of a 8-inch springform pan. Fill right away or chill up to 2 hours.