Ethereum can of course be a currency - anything can. The Euro is a currency even though Mr Draghi announced yesterday it was formally worthless by offering to pay people to borrow it.
Maybe what you "still don't get" is why researchers spent 20 years trying to come up with something like bitcoin in the first place. Up until 2009, there was no "gold" analogue on electronic networks - an uncounterfeitable token that could be directly transferred peer to peer in the absence of a trusted counterparty. The bitcoin phenomenon broke that duck.
The best that can be said about Ethereum in terms of store of value metaphors is that it's a leaky hot-air balloon. The "hot air" comes from the speculative expectation of accrued value. The "leaky" part comes from 2 sources:
[1] - the huge emission trajectory
[2] - the diverse range of investment targets that will be created by the ecosystem (i.e you're going to have to decide if you want to invest in the assets or the tokens and, although the capitalisation of the tokens will boost the value of the assets, the capitalisation of assets may not to the same for the tokens since many or most of them will be blockchain independent)
If Ether goes to $100, it will only do so if Bitcoin goes to $6000 IMHO. People are not trading the ETH/$USD market, they're trading BTC ratio who's trajectory is a whole different prospect from what you're citing. The bitcoin reward is getting close to halving. Ethereum, on the other hand is about to spew another 20 million coins into the supply over the next 12 months, shrinking your holding as a percentage of the coin supply by 28%.
What will people do in this circumstance ? One of three things:
[1] - use it to build assets, companies and blockchain-based products who's value DOES continue to accrue regardless of the value of Ether tokens
[2] - dump it into a true, store-of-value bearer token such as bitcoin (or equivalent such as Dash where it even earns a return)
[3] - hold Ethereum tokens, do nothing with them and watch them lose value against Bitcoin (even though they may gain value against the $USD)
...and that's exactly as was intended by the designers
Dude, Bitfinex is the first that jumped in and many others will do the same because they are bailing out of Bitcoin, they are at war. I'm talking about Coinbase, Circle, Xapo, etc. They won't jump ship in the next weeks but if Ethereum continues to rise and Bitcoin keeps the same stubborn attitude, they will be losing money and that's all it matters. They are not fanboys that think it's Bitcoin or nothing.
Starting next week you can buy ETH with fiat so expect MANY exchanges and new investors flocking in, that's a fact. Many people invested a lot of money in BTC but never handle a wallet or authorization key. BTC is actually holding ETH back in my opinion. When investors can get ETH with fiat at many exchanges and sites, ETH will rise to $50 or even more.