A great discussion, Lewm and Johnnyb. There is one playback scenario not mentioned, the one I use. I have a fair number of 50's and early-to-mid 60's mono LP's, and in addition to my main pre-amp I have been using one (ARC LS-1) with a mode switch having the following settings: Stereo, (Stereo) Reverse, Mono, Left (channel only), and Right (ditto). Using a stereo cartridge, a mono LP can be played with the mode switch set to not only Mono, but also to Left or Right, whereupon that channel's input signal will be fed to both the left and right outputs of the pre. Switching between them allows one to compare the two groove walls! The best sounding wall can then be the one listened to.
I also listen to early stereo LP's (particularly Beach Boys and Beatles) via the Left and Right inputs separately, to hear the extreme left/right panning on those records, with the instruments in one channel and vocals in the other. Many of the early Beach Boys albums were not offered in true stereo, but in Duosonic (mono reprocessed fake stereo). The two channels of Duosonic LP's can be compared, to hear the processing (frequency and phase differences added to the original dual mono channels).
A cartridge of particular interest for the playing of mono LP's, I believe, is the Decca/London, because of it's sum-and-difference design. The cartridge produces a L+R signal and a L-R one, to attain stereo. How that can be exploited for mono LP's I don't know.
I also listen to early stereo LP's (particularly Beach Boys and Beatles) via the Left and Right inputs separately, to hear the extreme left/right panning on those records, with the instruments in one channel and vocals in the other. Many of the early Beach Boys albums were not offered in true stereo, but in Duosonic (mono reprocessed fake stereo). The two channels of Duosonic LP's can be compared, to hear the processing (frequency and phase differences added to the original dual mono channels).
A cartridge of particular interest for the playing of mono LP's, I believe, is the Decca/London, because of it's sum-and-difference design. The cartridge produces a L+R signal and a L-R one, to attain stereo. How that can be exploited for mono LP's I don't know.