Fold two 18-in.-long pieces of foil into two 18x4-in. strips. Line perimeter of a 4-qt. slow cooker with foil strips; spray with cooking spray.
In a large skillet, cook bacon over medium heat until crisp, stirring occasionally. Remove with a slotted spoon; drain on paper towels, reserving drippings. In same skillet, heat 2 tablespoons bacon drippings over medium heat; cook pasta in drippings 2 minutes or until edges turn translucent. Transfer to slow cooker.
In same skillet, heat 1/4 cup bacon drippings over medium heat. Add flour, garlic powder, onion powder and, if desired, paprika. Cook and stir 1-2 minutes or until flour begins to turn pale golden brown. Gradually whisk in milk and broth. Bring to a boil, stirring constantly; cook and stir 1-2 minutes or until thickened. Stir in cheeses; transfer to slow cooker. Stir in pasta. Cook, covered, on low 2-3 hours or until pasta is tender. Top with bacon.