My $.02 is that when it comes to making something tough against sharp abrasive surfaces you need a tough and sacrificial surface. The graphite or aluminum can work but by the time you get a thick enough surface one could just as well have a tough fabric in the mix. And one that won't have to be dark and heat absorbing. A thick layer of resin with additives still won't provide the protection to scraping IMPACTS that can occur, scraping/abrasion yes, impacts no. I'd go straight to multiple layers of s-glass as the amount of durability to impacts AND abrasion resistance is greater than just resin and additives or resin and poly cloths. A couple layers of 6oz s-glass with a thick layer on top of fillcoats mixed with white pigment and a little cabosil will give a very tough surface with the top layer of s-glass taking the abrasion when the fill coats are scraped through.