My first thought was painting, but these items are unpainted black plastic so I'd rather save 'em. With nothing to lose I hit this panel with some 1500-grit wet/dry sandpaper and the spotting began to fade. Once I was back to black a final sanding with 3000-grit gave the finish I wanted. Next I wanted to get as close to the factory sheen as possible; not too dull, not too slick. Trying different rubbing and polishing compounds, I finally settled on a favorite all-around restorer, Meguiar's Ultimate Compound. Just a light hand polishing got me the result I was after.
These panels take a beating over time from sun and, commonly, brake fluid, as they sit under the brake and clutch master cylinders. They're also very difficult to find these days, especially in one piece. Project 20, a beautiful all-original VFR750, deserves the effort to save the original, unpainted panels. Mission accomplished.