I would be in favor of a epic level book. Not so much for the "set rules" but for ideas that I hadn't thought of before. I never really remember anyone I've gamed with going off the standard idea of a character. If somebody goes of the idea that a fighter can only be a muscular guy in big armor carrying a big sword, then I would suggest 4th edition. It would be my opinion to do something along the lines of the complete series in 3.5, just add epic progression to the classes. This would give variants for all levels of gamers. And I do agree that it is up to the DM to control the game. No matter what level you are playing at, it is possible to have out of control power gaming.