A spherical stylus has a large round contact with the groove wall. Elliptical has a narrower contact and is in the vertical plane hence moving more accurately with the groove at high frequencies and reducing distortion. So better HF.
A nude elliptical is an elliptical stylus that consists of only the ( tiny) diamond tip glued to the carrier tube ( the cantilever). Cheaper stylii are ( small diamond tip) stuck to a a tiny holder which is then glued to the cantilever. This means less diamond ( not really a problem ) but more mass due to the interface and inferior HF performance. Basically on cheaper cartridges.
Shibata has a finer sharper contact making it's HF performance even better. It can also easily collect more dust from the grooves and might need more cleaning than an elliptical or hyperbolic stylus. All stylii need to be cleaned periodically to remove muck that gets trapped on the rear surface of the stylus.
About " there are four varieties of MM cartridges " . No , there are several varieties of "stylii " that can be used on a MM cartridge . Like you could get a spherical or elliptical or shibata or SAS type stylii for the same cartridge. Not all cartridges have a wide range of stylii available for them. Prices keep increasing rapidly from spherical to fine line SAS types.
If the original recorded quality isn't first class and if the pressings are on average vinyl ( older Indian albums) then an expensive Shibata or SAS may not be worth it. But if you have the money, why not ?
If you have pristine albums ( 200 gm ) and/or albums from specialized manufacturers like Mobile Fidelity etc, then the Shibata or SAS will certainly be worth it.
However do note that bass/mid quality isn't the same for all cartridges. Read up reviews before you plonk down good ( large sums of ) money. If you are confused, just get an elliptical/hyperelliptical stylus. Also remember the sound is also affected by the performance of the tone arm on which the cartridge is mounted ! Things get more involved as you try to improve the performance. You should know when to stop . Otherwise your empty pocket will force you to stop the improvements. Analog can end up being VERY expensive if you are not careful !