Here's the offer on American - redeem $50 in GM card earnings (at 5% you would need to put $1000 on the card) and get an AA coupon, valid for up to 4 persons, worth -

$25 each off a ticket of $150-249 OR
$50 each off a ticket of $250-349 OR
$75 each off a ticket of $350-499 OR
$100 each of a ticket of $500 or more

So I guess it's just a matter of what you think such a coupon is worth. Obviously, it depends on how you use it.