I use new rims and foams every time. I recently did a comparison of a softer losi foam to a firmer AKA foam with the same tires and rims. I found that there was a big difference in handling with the firmer AKA foams. Foams can break down over time and therefore I would see no reason to use an old foam, the performance would not be there. I see the pros reuse foams all the time, it could be because they get their tires in bulk from their sponsors with no foams, IDK. But I can tell you that the firmer foam gave a performance advantage over a softer foam.