The thing i really like about volunteering at these events is that you get to see and hear the cars in action (as a marshall, you direct the show cars to their positions in the display area), and hearing some of those monster engines really gets the heart racing. As a member of the public at these shows, you just get the static display of the car, you miss out on the really exciting aspect of getting up close to these vehicles while they're running.
There is another show coming up on the 17th of May, being the English / European Car Show. I did this one last year as well, and I actually prefered it to the American show as the cars are more along the lines of what I, as an mx5 owner, would consider to be classic, proper sports cars, rather than the brutish American cars. The elegance and, errr, exoticness !??

Anyway, if this sounds interesting to you, i highly recommend you contact Jacqui on the above number and volunteer your services for the morning. Trust me, you'll really enjoy it.