The SCCA sets the National PAX Index after the Solo II Nationals each year. The idea is to pretty much do what you are suggesting -- level the playing field between all the various classes on an indexed basis, and they use the top National Level drivers to set that index. Of course, many things change throughout the year, and PAX adjustments are never perfect. But I like the PAX Index and the ranking it provides -- gives me an idea of what kind of driver I really am against all the cars/drivers at an event.
For what it's worth, Equipe Rapide has the 2005 PAX posted on their website: clickie.