I agree with nearly everything you said, but I disagree, fundamentally, with the bolded. Gold mining is not a waste of energy. It is the opposite of waste, it is the measure of value people place in the 'utility of having gold as a medium of exchange' or a store of wealth, jewelry around their body parts or connectors on their home theater system. If there was no demand for gold, the price would be zero. Hence it is not a 'waste,' by definition.
Not necessarily, digging out a little bit more gold just makes the existing gold a bit less valuable since the supply is increased. That is because its value is mainly derived from its scarcity. Its utility IS its scarcity. However, it is not a waste for the miner if the cost of mining can stay below the price of gold.
And it's scarcity is a product of its demand. Therefore, owing to the law of supply and demand which derives solely from human desires of turning "what is" into "what I want," any gold pulled out of the ground is a product of human desire, and, by definition is NOT WASTE. If the price and quantity demanded by the market are below the extraction cost for the miner then that demand will remain unmet. Again, this is the opposite of waste.
Ta,