I second the power washing and Woody Wax. Its worth a try and you can always remove the wax and paint it if it doesn't meet your satisfaction. We use it on my cousin's fishing boat and it keeps the non skid looking new. Easy to apply, follow directions.
I have used Penetrol on chalked gel coat. Looks ok when first done, but it doesn't last long and is a pain to remove.
Rehoboth Bay/Indian River, DE
S/Y KJ, Helms 25