There is a list of additional features
here, pro ACP screenshots
here, and a front-end demo
here.
Personally, it is hard for me to give you reasons to upgrade to pro without sounding like I am trying to get you to make a purchase. Maybe another customer can provide his/her opinions though. In the meantime, what I'd suggest is to check out the above links and surf around the lite forums to get a sense of the product.