Finally, you should tell us what is your favorite new MM cartridges and how many of those greatest vintage MM did you try and actually compared to the modern MM ? Also it would be nice to know which modern MM you could compare to some of your new LOMCI like the Grado cartridges. We use a Grado Gold mounted in our SL-1200 to play back tracks we've cut on our Scully mastering lathe. Its a sort of standard- if it can play it back, we've not overcut it. And we've shown that it has bandwidth past 35KHz mounted in that arm.
Anecdotally I've run a Transfiguration Orpheus for some years. One time a channel failed so I had to send it back. While waiting for it (or a replacement), I was jones'n for tunes and realized that I had a Grado Green (at the time, retail of $35.00) sitting new in the box. Since my Triplanar is very adjustable, I set it up and took the time to do it right. It was at this point that I realized that the ability to track the cartridge correctly was far more important than the kind of cartridge you have; the Green tracked perfectly although it sounded a bit 'up front'. Then I remembered that loading is critical on high output MM cartridges; once I get that right (using a 10K resistor) it was quite relaxed and other than having more output, was not significantly different from the Orpheus in any way I could discern. I threw some real torture tracks at it and it was effortless.
The main concern anyone should have using an older MM cartridge is that the suspension for the cantilever perishes over time; whether you are using the cartridge or not after 3-5 years it simply won't meet spec.