You could have a cryptocurrency without a block chain
Perhaps, but then you'd need to solve the problem of trust-less peer-to-peer Byzantine concensus a different away, using a different mechanism. And that's exactly why the blockchain is novel.
What something is worth depends entirely on its context and available substitutes (aka. supply/demand), for example a generator isn't worth that much under normal conditions as people have the grid as a substitute.
After a hurricane or something else that removes the grid as a substitute the generator is worth substantially more.
Ask yourself how much you think a lion would pay for your gold ring, house, or anything else you think has intrinsic value.
The nature of trade incentivizes individuals to find resources that are less valued by one person and more valued by another. For example starbucks finds coffee beans from farmers who don't find them terribly valuable, and sells them back to consumers who find them much more valuable, especially in conjunction with their value adds. Coffee beans are worth different amounts to different people, only when we make a transaction do we start to discover price.
Market valuations can become decoupled from intrinsic value, but that doesn't mean the intrinsic value is zero. In the long term if something really repesents zero value its market valuation will approach that.