Replacing silver is absolutely correct.
Not because of the resistivity of bulk silver, but because contact quality depends essentially on surface cleanliness and oxidation. Silver develops a semiconductive oxide layer. Not only in books and on tea pots: older computer memory modules had silvered contacts and did work unreliably.
Gold is THE proper choice for contacts. That's why the electronics industry is the second consumer of gold. Many people tried alternatives but failed. Well, rhodium and platinum would fit also...
Nickel is THE standard affordable barrier against diffusion that gets easily wetted by molten metals; at high (many MHz) frequencies, where nickel's magnetic permeability increases losses by skin effect, palladium replaces it.
Nickel might also bring some mechanical strength to contacts, which neither copper nor gold do, and this should improve the endurance for repetitive connections. Only a hypothesis from me.
To know if nickel is commonly used as a barrier, take an old component (say, a computer memory module) and abrade its contacts gently with fine sand paper. Look for a white metal at the transition between remaining gold and apparent copper.