I don't recall ever reading that a spherical tip is to be preferred for mono. Rather, I have often read that the spherical shape is OK for mono, whereas it would be regarded as out-dated for stereo. Miyajima make some of the best mono cartridges, and I believe without having checked recently that some of their models use spherical tips.
Mono cartridges come in two very different "flavors". Most modern mono cartridges are stereo cartridges in which the two channels are bridged, internally, to provide mono output into two channels of a stereo system. In that case, the signal derived by vertical deflection of the stylus is present but cancelled before it goes anywhere. Only a very few modern mono cartrides, like those made by Miyajima and maybe some of the Lyra mono cartridges, are "true" mono, designed so that they cannot read a stereo signal, which is to say they cannot read signal derived from vertical deflection of the stylus. Your Grace is vintage and evidently is of the latter type. So, I am curious, do you somehow run the output into both channels of a stereo system, or do you listen to it over just one speaker of your stereo pair?
Last year when I was in Tokyo, I bought a Shelter 501 series II mono cartridge. It has 4 pins, so is probably a bridged stereo type. I have yet to install it on a tonearm. I really should do that. In one of my two systems, the phono stage has a mono switch. Engaging the switch for mono LPs affords a huge improvement, and I think you will find the same at least with your mono cartridge, on mono LPs. Using the mono switch on a phono stage is really just like using a bridged stereo cartridge that produces a mono signal into both channels. I've wondered whether it is even better to use both a mono switch AND a mono cartridge, for mono LPs.
Mono cartridges come in two very different "flavors". Most modern mono cartridges are stereo cartridges in which the two channels are bridged, internally, to provide mono output into two channels of a stereo system. In that case, the signal derived by vertical deflection of the stylus is present but cancelled before it goes anywhere. Only a very few modern mono cartrides, like those made by Miyajima and maybe some of the Lyra mono cartridges, are "true" mono, designed so that they cannot read a stereo signal, which is to say they cannot read signal derived from vertical deflection of the stylus. Your Grace is vintage and evidently is of the latter type. So, I am curious, do you somehow run the output into both channels of a stereo system, or do you listen to it over just one speaker of your stereo pair?
Last year when I was in Tokyo, I bought a Shelter 501 series II mono cartridge. It has 4 pins, so is probably a bridged stereo type. I have yet to install it on a tonearm. I really should do that. In one of my two systems, the phono stage has a mono switch. Engaging the switch for mono LPs affords a huge improvement, and I think you will find the same at least with your mono cartridge, on mono LPs. Using the mono switch on a phono stage is really just like using a bridged stereo cartridge that produces a mono signal into both channels. I've wondered whether it is even better to use both a mono switch AND a mono cartridge, for mono LPs.