Don't do anything to the horn. Consider it art and play it proudly. If you need a shiny horn, buy a second instrument. for what it will cost to return your old horn to shininess, you can get a fine used horn. Buffing all of the scratches out could change the sound as the material will get thinner where the most damage was done. - on the other hand, a splotchy "camouflage" finish could also be considered art.