Preheat oven to 350 degrees. In large bowl, beat butter with 2 cups sugar until well blended (mixture may not blend together completely). Add eggs, one at a time, beating well after each addition. Add flour, baking powder, soda, buttermilk, and vanilla and beat until combined. Stir in walnuts and thoroughly drained pineapple.
Spray two 9 by 5 inch glass loaf pans with nonstick baking spray. Divide batter among pans. Bake at 350 degrees for 55-65 minutes until loaves are browned and toothpick inserted in center comes out clean.
In small bowl, combine 1/2 cup sugar with 3 tablespoons reserved pineapple juice and mix well. Drizzle this mixture over the hot quick breads. Let stand for 10 minutes, then run a knife around the sides to make sure the bread is loose from the pan. Carefully remove from pans, place on wire racks, and let stand until cool. Store tightly covered at room temperature.