I have over 20k miles on all of my aluminum pulleys. The v-belt ones have almost no wear showing however the 8mm blower pulleys have about 1 more year before they will have to be replaced. My mistake for not getting them with hard anodizing. Apparently the lower pulley gets sand and road grit trapped in it and the stuff goes around and around doing it's thing. The blower belt shows no wear at all.
I put a direction arrow on each belt so it gets installed going the same direction each time I remove them. Whether it does any good or not I don't know. It's just an old habit from industry.