Originally posted by Ira Speak for yourself--that was MY problem! (Just joking.)
I had a Mamiya 645 in the stone ages, and the economies of scale are a killer. (Plus, handheld, forget it. A PITA.) Yes, MF shooters slow down to be more careful about each image because of the cost and practicalities of film loading, but the basic rule of photography still applies:
The more frames you shoot, the better your chances of getting more great ones.
Your last sentence may perhaps be true for the few sports photogs among us. But in general I would really disagree. The number of shots taken has no fixed proportion to the number of shorts that were worth taking. Especially these days, when digital images cost nothing at all, people replace composition and looking for the right moment with machine gun photography - and the outcome surely is not a high amount of "great ones".
Also, I don't agree with your second paragraph. I use my Mamiya 645 very often handheld. At the end of the day, it is not that much heavier, than an K20+ grip + QR plate + lens. But indeed with longer focal length lenses, I long for the tripod earlier, than I do with 35mm or APS-C digital.
Ben