Best XLR cable and metal for home use & vocals?
This is all marketing bullshit meant to confuse you. As a plain customer, you cannot evaluate the thickness or durability of the contact plating anyways.

What's important for microphone and other pickup cabling is the mechanical stability of the connectors. Both the contacts and the housing, so you don't pick up noise from the contacts as they move. XLR is much better than other connector types in this regard already, but I have to assume there are also cheap types out there. Most likely those covered in 0.5µm gold.

Contact plating is your least concern. Nickel is ok. The cheap gold plating on "high end" connectors is scratched off from the contacts anyways as soon you plug them in, exposing the nickel undercoating.