I do think that is useful as a rough metric. Right now, like it or not, "fiat" is still "real money" in the sense that it is the only transactional token accepted EVERYWHERE without question. Bitcoin and PMs only become "real money" when they too can be used universally in all everyday transactions.

So we have to separate the notion of "transactional token" from "store of value". I myself believe that bitcoin is still far too volatile to serve as a reliable store of value. If it eventually overcomes that drawback, it will no doubt be priced much higher, and some will beat themselves up for not buying it when it was "cheap." But that mentality takes us back to viewing it as an investment (IMO a speculation) and not a stable store of value.