Thank you, Ruben. The more I read, the more I'm thinking that the two cameras complement each other fairly well. Each seems to have strengths not present in the other. If I need to take complete manual control--if I want to shoot IR, for instance, the Konica is the clear choice. If I want to shoot a lengthy low-light exposure, from what I've read, the Yashica shines. The Konica's shutter is not excessively loud, but the camera has been justly criticized for its unnecessarily loud ratcheting wind lever, so the Yashica would be the choice where quiet operation is necessary. (It's funny that they both have mercury battery replacement issues of very different sorts, the Konica not having a problem finding a battery of the proper size but of the proper voltage, the Yashica on the other hand dealing well with the difference in voltage but needing help with appropriate fit.) As for the yellow patch, I've found a bigger problem with the Konica's viewfinder being a tendency for the half-silvered mirror to fall off its mount as the adhesive ages.
Happily, they both take the same size filters . . .
So in the end I think I'll be happy to have both. I was thinking too much of where their abilities overlap, rather than where they don't.