From the perspective of appearance any parts made with non UV stablised epoxy resin systems, which have not been clear coated, are going to start to discolour relatvely quickly, especially so in locations which are very sunny.
In general the only UV stabilised epoxy systems easily available are intended for surfboard production, and are more costly than non stablised material. Most people producing cosmetic carbon motorcycle parts on a commercial basis, use pre-preg materials, and clear coat the finished parts.
Unless a customer is familiar with composite work, he or she is unlikely to be able to tell if a part has been made with poly or epoxy resin. Whether or not the finish of a part degrades quickly is more likely to have to do with not using the correct material in the first place, or not using it properly, rather than the resin system used.
Either system will work fine, but need to clear coat, longer process time, and additional costs, suggest that anyone wanting to produce parts for retail, should think very carefully before opting to use epoxy resin for non structural cosmetic motorcycle parts!
