Preheat oven to 350º. Beat cream cheese and butter at medium speed with a heavy-duty electric stand mixer until creamy. Gradually add sugar, beating until light and fluffy. Add eggs, 1 at a time, beating just until yellow disappears. Add sweet potatoes, and beat well.
Stir together flour, next 3 ingredients, and, if desired, cinnamon in a medium bowl. Gradually add flour mixture to butter mixture, beating at low speed just until blended after each addition. Stir in vanilla. Spoon batter into 2 greased and floured 8 1/2- x 4 1/2-inch loafpans.
Bake at 350º for 1 hour and 5 minutes to 1 hour and 10 minutes or until a long wooden pick inserted in center comes out clean. Cool in pans on wire racks 10 minutes. Remove from pans to wire racks, and cool completely (about 1 hour).