Is higher capacitance necessarily desirable in a tonearm cable?Hi Lloyd,
Absolutely not. Assuming that you are referring to a moving coil cartridge, the reverse is more likely to be true. See the post by JCarr here.
If you are referring to a moving magnet cartridge, then having either too little or too much capacitance can adversely affect tonal balance. The total of the wiring capacitance plus the input capacitance of the phono stage should approximately conform to the load capacitance recommended by the manufacturer of the particular cartridge.
Also see this paper.