I received the promotion too, except the bonus schedule is completely opposite then what you describe. For me, if I spend between $1-8,500 I receive no bonus miles, from $8,501-13,000 I get .25% of 1 mile bonus, $13,001-16,500, I get .5% of 1 mile bonus, and finally $16,501-$50,000 I finally get the 1 bonus mile for every 1 dollar spent. So its really not worth it, unless I plan to spend atleast $8,501.00 by December 31.

This is opposite of what you seem to be getting, so anyone else want to chime in and let us know what promo you received.