You might want to read the stuff at if you haven't already.

In particular the archive of Mike Johnston's articles. There is one in there on large format photography that is sort of apropos to your problem in a round-about sort of way:

In my opinion, there isn't much difference in sharpness or detail between medium format and digital, but that is obviously up for debate. Having already drunk the digital kool-aid I'm not sure you would get any benefits out of medium format. Large format might make more sense, but it all has to do with what you take pictures of, what processes you like to use, etc. Each format has its own strengths and weaknesses.