Let me first say that I am not associated with Aurora in any way.
That said, try Aurora Boat Scrub on the non-skid prior to applying the Sure Step. Apply with a scrub brush, then thoroughly rinse, and watch your non-skid look brand new again with minimal effort. This stuff works great. The product contains a harmless leaching agent intended for gelcoat use, and once you start, you will want to do the entire non skid area. Otherwise, the area you "touched up" will look new, and the rest will not.
Follow up with a Non Skid specific wax, and you won't be scrubbing for a while, as a rinse will do it.