Wash spinach thoroughly. Spin or pat dry. Fry bacon over medium heat until it begins to crisp. Drain on paper towel. Reserve 4 Tbsp of bacon drippings.
Return pan with drippings to heat. Meanwhile, whisk together cider vinegar, maple syrup, salt and pepper in small bowl. Add mixture slowly to bacon drippings. Stir well. Remove from heat and let cool slightly before adding sour cream or yogurt.
Arrange spinach on serving plates. Fan both types of apple over spinach, sprinkle each plate with bacon pieces, raisins and walnuts. Spoon a little dressing over each and serve immediately.