Value is whatever we decide it to be. However, there are certainly things that can be safer bets for holding value than others. Precious metals for example, as well as other natural resources, get their value from their practical use. So I can safely assume that tomorrow that value will remain fairly steady, barring a global catastrophe such as an asteroid strike or nuclear war. For the value of such a thing to disappear would require a massive shift in human technology and culture.

There are of course things with value that are far less certain. Tulip mania is a great example of this. Value was driven entirely by societal demand rather than practical usage. This led to a wildly speculative value that diminished as quickly as it rose. Value that is backed by culture only is volatile as cultures can see radical shifts over short periods.

As for how this relates to cryptos, it's a bit of both. There are real world practical uses that these currencies support, but there are many coins that are simple copies that really fail to reach that practical usage. People are still figuring out this new world, and it's a mixed bag of precious metals and tulips. Over time the tulips will subside and the ideas backed by practical value will endure and grow.