Fans love the Bottoms Up system, and the souvenir MAG™ space; incrementally more with quality designs. Fans have been spotted going through garbage cans looking to see if anyone left behind their MAGs™ - yes really. They are trying to either collect their set or simply have an additional souvenir. Those are great ways to improve the perceived value and fan experience.
One way to improve the fan experience is to give them an opportunity to come back. These paying customers are sitting in their seats and drinking their beer (a quality customer in our mind) and what a great time to ask them if they want to:
We think you get the idea, but the value is to capture all of the people interested so your ticket sales department can follow up with those leads and increase attendance - particularly of those fans having at least one beer… There are many ways to capture this information without becoming cost prohibitive, for example:

Direct them to a contest entry location with paper submission forms like your merchandise store or near select concession stands, which can only be filled out at the stadium; or a sponsoring company location