Any one should look to attend. You are standing right off the edge of the rocks and competition, though still far enough away for safety purposes. Bring a chair and great boots. The rock surface is hard on the calves and heels and the lower back (I must be getting old). Also beware of the hot air on the sunny days. There is some air movement, but really nothing there.
You can watch several races at one time from one spot. Its setup for the viewer as well as race participator. You'll have fun and be amazed at the crawlability and angles they take.
Its rather cheap to attend as a viewer (can't remember the cost, but recall thinking that's it'). Then there is food and drink available. It is really cheap and sold for the local firehouse IIRC. 4x4directory is a forum for the rrock series at Hannibal.
97 TJ SE lifted, locked and rubbered for fun
94 YJ SE stock, 225s, Trail Tested