Being a campus rep is a lot of fun! You get to keep all your connections to Disney while you are back at school. If your school is bigger and has other reps its nice to know other people at you school that have done the program and are going through the same things as you. ( Leaving is the hardest part of the program).
I love sharing my experiences with other students who are considering going. and then meeting the people who got accepted and answering all their questions. There is a min amount you have to do, but really it is all about how much you want to put into it. I like knowing that they more we do to promote it on campus the more popular it gets and advisors are more aware of the program, making it a little easier for students to get credit.
as far as the interview, just highlight what you've gotten out of your program and what you can bring to new students thinking about the program. any team work and leaderships examples are good too! Good Luck!