I've heard people say they like to have a medical because they value having an MOT every few years, whereas my impression was that the class 2 wasn't too concerned with your general health, and was more concerned with whether you were likely to suffer from faints, fits or funny turns and had halfway decent visual and auditory perception. I have worried that this may sometimes give people a false sense of security.
This seems to be reflected in this thread, and it strikes me that the medical could be combined with a few additional tests in order to give a 'wellness check' of the sort that BUPA do, along with some lifestyle advice etc. I probably wouldn't go for it myself (and still not entirely sure that I believe in them as a concept), but I could see it working as a commercial proposition.
I'm also uncertain about how much information gets passed back to GPs from class-2 medicals. I presume that most AMEs would write to a GP if they discovered evidence of any dread disease, but what about routine blood pressures etc... It seems disjointed to me to be collecting health data under two separate systems. Fine if you consider only that the class 2 is a pass-fail for the purposes of aviation, but potentially messy if it is considered as healthcare.