Is the non-skid from the factory? Or is this something the former owner put on?
Sounds like someone might of put a coat or resin or poly/epoxy paint on and dusted it with sand while it was still wet. Why not leave it if you can? Take some 120 wet/dry and just take some of the “tooth” off of it? I have seen more boats ruined by disk and belt sanders in the hands of inexperienced people than from any other cause. It is risky enough with some one who has a lot of experience, for someone with little or no experience it usually ends in disaster. They usually end up sanding thru the gel coat and weakening the underlying glass. Your Tornado has very thin skins as it is; to attack it with course sandpaper on a disk/belt sander is a recipe for disaster.

Bob