Combine the first 3 ingredients in a bowl; cut in margarine with a pastry blender until mixture resembles coarse meal. Set streusel mixture aside.
Combine 1 1/2 cups flour and next 6 ingredients in a bowl; stir well, and set flour mixture aside.
Combine the nonfat buttermilk and next 4 ingredients in a large bowl; stir well with a wire whisk. Gradually add flour mixture, stirring just until dry ingredients are moistened.
Pour the batter into a 9-inch round cakepan coated with cooking spray, and sprinkle streusel mixture over batter. Bake at 350° for 40 minutes or until a wooden pick inserted in center comes out clean. Serve warm.
Note: Dried, pitted tart cherries are available at specialty-food stores and large supermarkets or they can be mail-ordered from American Spoon Foods Inc., 800/222-5886. You can substitute raisins, chopped prunes, or dates for the dried cherries.