Thanks for the advice, guys. It's all food for thought.
Bruce: No cataracts. Very nearsighted, though, plus
the other usual maladies.
Peter: The Bessa is an R4M, so its VF magnification is about the same as the RF's. I find the RF is a bit more finicky to focus, but, on average, the R4M is just as problematic. Of course, the weaker the light, the bigger the problem.
Dacaccia: I've worn glasses for decades. These days, they're compressed progressives.
Ruben: Thanks for the interesting diopter twist. As you say, the combination of a camera's design with each person's vision results in a unique situation. I've resisted putting a diopter on the camera because I've never seen one with a sufficiently powerful correction factor (I'd need a +4.0) and because I don't want the hassle of constantly putting my glasses on and off.
I'm gonna let this play out for a while in an effort to determine what's really bothering me. Right now, I'm not sure if I'm being bothered by dimness in the VF or by the negative magnification of the RF and R4M. Or, both. I do know that I spend more time than I want trying to focus, and that I rarely have the experience of the image "clicking" into obvious focus. Typically, I acquire what I think is the right focus, and then move the lens back and forth to check.
In any case, the problem is taking the enjoyment out of taking pictures, so something has to change. It is not fun to futz with the focus ring, seemingly forever, only to press the shutter with very little confidence that I have, in fact, managed to put the subject in focus.
Going to autofocus would almost certainly mean going SLR. Frankly, the only downside to that, from my perspective, is the doubling of the size and weight of the stuff I'd carry around. My attachment to rangefinders is practical (size, weight and simplicity), not emotional.