The value of the work done in the Blockchain must be tied to the value of the applications it supports. This was always the premise from day one. Originally, that application was supposed to be payment processing. A perfectly legitimate application, but one which comes with an interesting problem - it requires an external source of value. The value of a payment processing application can't be more than the value of the assets it can process. Also the Blockchain turned out to be pretty shit at it.

The speculative value of Bitcoin was always a paradox, and pretty obvious IMO. But cryptocurrency as collateral value for stake/work done in a distributed applications is legitimate, and some variant of it will eventually find some valuable application IMO. But those tokens will need to have stronger anti-speculation mechanisms built in.