I don't think the prize is of major importance either - it's the buzz and the personal satisfaction of presenting winning designs in a fun contest.
I recall (I think it was Club Spades on one of the major poker portal sites - was it Cardplayer?) T-shirt contest last year which generated a huge amount of interest and some really great and clever designs...not to mention site traffic
Perhaps the momentum will build as the competition becomes more widely known and the choice of designs submitted by the players grows.