I’m a "one ear" since the age of eight. I don’t hear stereo and have no directional hearing except by trying to discern the direction of the loudest sound. I do, however strive to make my hi-fi sound the way music does in the concert hall or opera house. A forlorn struggle, but there’s no reason not to try. So I’m good at analysing the quality of sound, if not the solidity of the stereo image.
Having some mono LPs, not so much deliberately collected as just acquired along the way. They go from 1951 Furtwangler up to mono releases of the Beatles and Moody Blues in the late 60’s. Having discovered for myself that proper record cleaning is the biggest upgrade of all, I was intrigued to learn that a mono cartridge sensitive to lateral movement only could reduce surface noise dramatically, and be more dynamic. I had to find out, and I believe it is true. True enough that having bought one decent mono cartridge I’m now getting an old favourite stereo cartridge rebuilt as a true mono pickup just to see if it will be better still.
All this is entertaining and fun, but if I weren’t mostly an analog guy I don’t think I’d bother. I have some mono CDs, but when I had a mono switch (I don’t now) I couldn’t tell the difference when playing them. I do use Y-connectors rather imaginatively to make my headphone amp feed both signals into both ears, otherwise I’d hear only one channel and that’s no good.