It would be nice if:
a). Some of these posts had anything to do with Ethereum or Ethereum mining and
b). if posters had read at least the last 50 pages of this thread and/or some of the OT Bitcoin thread
No, cryptocurrency and similar (fun fact: XRP isn't cryptocurrency!) won't "all go to $0". ETH in particular is NOT a unit of digital currency. You can try to use it for that purpose, but that was never its intended design. It is a share of computing time on a world computer. Nothing more, nothing less. Its current price is a speculative guess based on the future value of said world supercomputer.
Since some people here seem to be struggling with the concept of how Ethereum (or any other crypto project) could have real-world value. Just one possible application of Ethereum: replacing all credit card and interbank payment systems, worldwide (caveat: XRP has a head start on the banks, though I'm not sure the banks like its centralized nature). How much do you suppose that's worth, per year? Here's a hint: it's in the hundreds of billions of dollars, if not more. And that's just ONE possible application for Ethereum, which it may (finally) have the throughput to realize in 2019, thanks to OMG/plasma networks and sharding.
And, for reference, if ETH/OMG works out properly and dominates back-end payment processing, you will probably never notice it at point-of-sale terminals. You will still do your buying and selling with USD. It might or might not be tokenized in some fashion. Don't expect to just "buy things with ETH".
Currently, there are 101,413,782 ETH tokens in circulation. How much are you willing to pay for one of those, based on the near-future potential of this blockchain?
That is why it has value. Personally I think people are paying too much for them right now, and that the EF has to prove itself, hopefully very soon. But the value proposition IS there. At this point, it's a speculative bet.