Are there metrics to measure how much is Bitcoin used to buy stuff? I totally see why merchants tend to integrate BTC as a payment method, but in the end it's for now use as long as most people go crazy about the last ATH.

I see how Bitcoin can fill a nische and I believe it's mere existent is important, but I doubt it will ever get general relevance outside of the investment market.
I mean, who would even consider to sell Bitcoin to buy a new car, at the moment? Or even the daily coffee? You might use a system with a middle-man that changes your USD into BTC instantaneously to buy a coffee, but that negates any potential benefit of Bitcoin as well so you could just use your regular credit card.