The reason I mentioned other forums is that I'm guessing that both General and Road have more people with RAGBRAI experience than this forum. But you'll note that I still haven't moved the thread and don't intend to. OTOH, if someone who thinks five miles is a long ride shows up in this forum it's going to General in a heartbeat.
I think people that can ride 20 miles regularly probably will have no trouble finishing RAGBRAI. So it's not like strict training and preparation is fully necessary. But I like to obsess and over plan with the best of them, so I can't complain.