Curbs always show wear more because they are usually textured and have lumps and bumps on them, and because the black rubber marks stand out more. See these pictures attached. I think Lynce has it correct. After a good race the track will look less clean because it will have tyre marks on it. You can see in the photos that the curbs are very worn and marked, but the track is very clean and new, and these are after F1 races where the curbs are usually painted just before the race weekend!
A further comment, I think the one thing that is missing from all Hi-res texture packs, is the trees. These always stand out when racing as being the 'weak link' and I think it is great that you are paying attention to them.
I would also like to draw to your attention, the Hi-res adverts that I added to for Fern Bay a while back http://www.lfsforum.net/showthread.php?t=70874
A further comment, I think the one thing that is missing from all Hi-res texture packs, is the trees. These always stand out when racing as being the 'weak link' and I think it is great that you are paying attention to them.
I would also like to draw to your attention, the Hi-res adverts that I added to for Fern Bay a while back http://www.lfsforum.net/showthread.php?t=70874