Preheat the oven to 400 degrees F. Line muffin cups with muffin liners or spray with nonstick cooking spray.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, ginger, nutmeg and allspice; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugars on medium-high speed until light and fluffy, about 2 minutes. Add eggs, one at a time, beating well after each addition. Beat in vanilla extract. Lower the mixer speed and add the pumpkin and buttermilk. On low speed, beat in dry ingredients. Using rubber spatula, gently fold in raisins and walnuts.
Divide batter equally among prepared muffin cups and sprinkle with pumpkin seeds. Bake until muffin tops are golden brown, 20 to 25 minutes. Set on wire rack to cool slightly, about 5 minutes. Remove muffins from tin and serve warm.