I agree when sanding you need to progressivly get lighter in gritt( higher number). once you get up to 1200 or higher I would normally say compound and then polish but those grey panels like to turn colors when you put wax or polish on them so you may want to try cleaning it and using a plastic shine spray (for trim). . Also for future reference (something I picked up while doing body work) for spray paint, rub marks from other cars and or objects pick up a can of specialty reducer(used to thin paint before spraying). Put on some rubber gloves as this stuff is pretty bad for your health lol, put it on a rag and just wipe away the marks. Works 98% of the time on most of the above listed issues.