A clay bar removes overspray. Try polish on the dirt that won't come off. If that doesn't work then try rubbing compound (polish should do the trick). As for the scratches, depending on how deep they are you might need to have the panels repainted. If they are not very deep you can try sanding them out with high grit sandpaper, finish with 2000-2500, but you'll need a high speed polisher and rubbing compound to get the sand scratches out. High speed polishers run around $200