Tried everything under the sun to remove scuffs, fill in scratches, rejuvenate faded areas on my grain-vinyl covered amps until I discovered good old (paste-style--not liquid) black shoe polish. Unbelievable coverage and finishing with a typical soft bristle shoe polish brush, the polish residue is completely removed, leaving a dull but reasonable shine (without looking like you just Armor-All'd it) and the black base of the shoe polish fills in and hides all but the paint-based scratches (you know: rubbing the amp along that white trimmed bar table).
One piece of advice when applying: Use a T-shirt type rag and moisten it before swirling into the shoe polish tin to get some material for applying. Then apply the material in a circular motion on a 6 inch area of the amp. Don't do more than 1/3 or 1/2 of one flat area before wiping vigorously with another dry rag/towel. Then finish by buffing with that soft brush.
Sorry for the late reply.