At least in 'Earthshock' gold worked the way it was supposed to (The Doctor had to grind it into the chest panel to clog up the system).
By 'Silver Nemesis', gold had turned into silver-bullets, you just had to shoot it into a Cyberman to take it down.
Yeah, the original idea was it's non-corrodable and so plates their breathing apparatus and suffocates them. By Silly Nemesis gold coins explode on contact with them!
None of the gold coins exploded on contact, in fact you can see thee Cyberleader take the coin out and get back up.
Which is itself contrary to the explode-in-showers-of-sparks that they've done through the story until that point!