All financial instruments are speculative. The fundamental value is only ever part of the question, because fundamental value divorced from resale value would likely never pay itself off for most investments in most people's lifetimes. Even Warren Buffet speculates on price, because he takes a bet on fundamental value
relative to market value.
You think cryptocurrencies are not investments because they aren't economic producers. Cryptocurrency is not an economic producer, because currency is not an economic producer. It is an economic enabler though, and currencies have intrinsic values related to their various properties that affect how they enable economies: backed by gold, backed by government trust, backed by cryptography, identity and trust in the controller of money supply, anonymity vs transparent identity, transaction speed, liquidity, legal legitimacy, etc.
The best historic analogy for the investment profile of the cryptocurrency craze right now is war bonds. With war bonds, you are investing in the success of the nation issuing them. Failure of that nation means default. Success means that bond is convertible to national currency that has a liquid marketable value. Right now the utility of those cryptocurrencies is low: transaction volumes are low, liquidity is low, acceptance is low. But by speculating on cryptocurrencies, you are betting on their future utility, with the caveat that most will likely fail and be completely worthless in the long run. Yes, it's speculative...just like every other investment out there.