I use some funky boat polish with silicone and UV retardents in it, it`s supposed to protect from UV and increase hull speed!
Is your board finished in glass or P-tex? If it`s P-tec, dont even try to polish it! You might be better off with some snowboard wax.
My board still gets scratched but at least it doesn`t get sunburnt,lol, can`t say that it goes any faster either.