I've found success selling the ones I don't use on OzBargain. As long as the offers roll in, just know there is a market place for ones you don't need, energy ones, Harvey Norman even baby bunting.But only if you actually need them and use them all.
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Then there is selling the statement credits at probably a 20-30% discount. These should cover the annual fees assuming you have the 5 cards per amex.