Marketing payback is a hard thing to calculate.  At the the end of the day, its hard to calculate the value of increasing name recognition, having people talk about you, and such.  Dropping down to the hard dollar costs and comparing the money that comes in versus the cost of the tshirts, we're looking at a 130x payback on the tshirts and the "More Wally" slogan.  I'm thinking this was probably a good investment.  Expect to see more variations on the theme.