I don't think it is the leather itself but inclusions that you pick-up from general use. You may not be able to see them, but dirt & grit gets imbedded into the leather.
Don't add anything into the leather -especially gunleather as this may ruin the molded shape of the holster. Treatments & cleaners will also make it easier for even more junk to imbed into the leather.
As to the steel, if Flitz doesn't work, you may need to use 2000, 1000, 600, 420 or 320 grit wet/dry emory paper to restore the satin 'grains' of the steel polish. Be careful that you don't scratch the steel even more.
For me, as long it is a 'using' knife or carry gun, I don't mind the scratches as it is considered 'charachter'.