Here are my thoughts... If you have gel coat, it is like sanding concrete, but it is hard. If it just lacks gloss, sand it all over with 1500, then 2000, then get a big, real buffer and buff it with a microcut and glaze. something that will remove scratches above 1500. Now, if you want a serious new shine, take and sand that gel coat with 220, then 440 with a DA, or random orbital sander. Then take a sanding block and wet 600 sand it, then sand it with 1000 and 1500. Now go spray a urethane sealer, then a solid urethane color coat, then 4 coats of urethane clear coat. Wait a couple of days and take 2000 grit wet sandpaper on a block to that clear coat. Then take a micro cut compound and glaze to it with a powerful buffer. You will take all that orange peel out of the urethane and make it look a quarter of an inch deep.