Where i have raced, the ozite has been fine except for the places that have used rallyblocks and minipins, there it was horrible in parts and probably due for replacement.
Jaco say i believe that your foams should wear fairly quickly when they are in the zone of most grip, but once they are just outside that they seem to last ages with allmost no wear. I know myself and fatdoggy have run small foams with no ill effects.