I don't think you can exchange your rewards for disney dollars at the parks. They're not even supposed to do it at the Disney Store, according to Bank One, although many of them do. Bank One said it's in the terms that come with your card, that the rewards "may not be redeemed for cash or its equivalent" (I looked it up and it's in there). Disney dollars are a cash equivalent. I think the parks will probably be far more strict about this than disney store.
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