Gold has other uses - jewelry, electronics, chemistry, healthcare. Even without it being used as a currency, there will always be demand for gold for these reasons. Now, if bitcoin could not be used as a currency and could not be spent anywhere, why would there be any demand for it? It cannot be used for anything else (or at least, any other purpose for it is exceedingly inefficient).
The price of gold has nothing to do with its usefulness, it's more related to the hoarding of gold by banks, states, ...
And I see this similar with bitcoin too: I don't think that those hoarding it as a store of value would care much whether bitcoin is used as a currency or not, as long as they can use it as an asset, even if not traded so often (and bitcoin price is also a result of hoarding more than actual usage).
And with the rise of LN, with far too many keeping their coins in custodian wallets, the users who want to spend may soon not even use bitcoin, they may use IOUs without knowing it.