Cook the elbow macaroni in a large pot of salted water according to package directions, but subtract 1 minute from the cooking time for al dente pasta. Drain thoroughly in a colander and rinse under cold water to stop the cooking process immediately.
While the pasta cooks, dice the red bell pepper, celery, and red onion into uniform small pieces (approximately ¼-inch cubes). Shred the carrots using the small holes on a box grater. Chop the parsley just before mixing.
In a large bowl, whisk together the mayonnaise, sour cream, apple cider vinegar, Dijon mustard, sugar, celery salt, garlic powder, and black pepper until completely smooth.
Transfer the cooled pasta to a very large mixing bowl. Add the diced vegetables, pickle relish, and chopped eggs (if using). Pour about three-quarters of the dressing over the mixture and gently fold everything together with a rubber spatula.
Cover the salad and refrigerate for at least 30 minutes to allow the flavors to meld. Just before serving, stir in the remaining dressing, taste, and adjust seasonings if needed. Sprinkle with paprika and additional fresh parsley if desired.