I'd be wary of any process (like sanding) that would remove the surrounding finish. Might be better off looking at a product that would just darken the scratches and reduce their visual contrast; I had great results with 303 Aerospace Protectant on some sun-cracked and faded A-pillar pads, they're obviously not the same material as a shroud, but worth a try. Also might try black shoe polish on a rag? Otherwise I'd just live with it, as an original part of your car with character!
