The long-term drivers of cryptocurrency prices
So what does it take for a cryptocurrency to be valuable in the long-term? In my book, it has to have one (or both) of two simple properties, which I'll describe in detail below.

Useful as a store of value. This property means that a coin is useful as something you can keep your savings locked up in. In that sense, it's the "gold 2.0" use-case, and even though I think it will be a driver of the long-term value of one or a few coins, I don't really take this property very seriously when considering whether or not to invest in a coin. Why? Because I'm not really interested in speculating on or investing in gold 1.0 (i.e. normal gold). Yes, some people make a lot of money doing that, but at the end of the day I don't want to spend my life being a judge in a Keynsian beauty contest . That being said, I want to make it clear that I do think this will be a big driver of the price of at least one cryptocurrency asset in the future, and for that reason I can't deny it as a driver of long-term prices in general. Why do I think it's a factor? Because the fact that gold has been popular for literally thousands of years as a store of value leads me to believe that society will most likely find it useful to have a digital store of value, and I think cryptocurrencies will serve this need extremely well. So what price can we ascribe to a coin that we think would be useful as a store of value? Like I said, I don't really think you can easily price something like gold in a rigorous way, but people who believe in the utility of stores of values would give you the following upper bound on a cryptocurrency's price, solely based on the store-of-value use-case:
Assume a single cryptocurrency, say bitcoin, completely replaces gold, which currently has a market cap of ~7.6 trillion USD. Yes, this is a wild assumption, but we're computing an upper bound here.
Take the total number of coins issued for this cryptocurrency. In bitcoin, the number of coins is capped at 21,000,000.
If the coin replaces gold, we can compute an upper bound for its price, assuming people don't lose millions of coins, by simply computing (market cap of gold) / (total number of coins). For bitcoin, this would come out to ~$361,904 per bitcoin