There is an extra forum for premium members that is private and you can also do classifieds if you want to sell or buy stuff. I was premium or platinum (don't remember them now) before I was asked to be on staff. I didn't even know exactly what the extra perks were. I just wanted to help donate to the site because I know how much costs and time goes into running a very very small site, let alone one of this magnitude. This forum helped me so much as a pre-nursing student and a nursing student that it was my way of giving back. I know there was the avatar, more private messaging, the ability to edit posts.
As staff there aren't any extra perks, it's a volunteer basis. Well it's not thankless, I guess I didn't word that right. They are very appreciative of the help. There is a link that explains the AN Guide. I will find it and post it. I think they get free premium membership and they also help with reporting posts and giving guidance and advice to other members.
If you find this site helpful and are able to afford it, I would definitely upgrade membership. You also get free of ads which I never realized how nice that was because I always paid for premium membership since I finally joined and stopped lurking. Well the other day I logged on from somewhere new but at first I forgot I wasn't logged on. I realized when I was thinking "where the heck did all these annoying ads come from" lol