I'm actually kind of torn on this one.
On the one hand, selling your leftover souvenir soda cups of a horrible-idea-gone-even-worse trade, smacks of Grade A douchebaggery.
On the other hand, if the buyer knows his $6 soda is going to have last year's "star" on it, instead of this year's "star" (ahem, Rex Grossman?) and he still happens to admire said person no matter whose team he's on.... well... then what's the harm.
I suppose this is better than 50,000 little starving kids in Africa getting the old McNabb cups and having to use them to dig ditches for their straw houses because they not only don't have any soda to put in them, they barely have any water.