EDIT: Just to address your edit...
> On EURUSD, you could look at currency funds (not strictly the same, but as close as it gets)
And will they be willing to talk to a person that only wants to put 100 EUR + 100 USD into it? I seriously doubt it.
All this means is there is money to be made. It does not mean that any particular use-case exists. So no, this does not make it hard to hold on to the idea above - no use-cases outside of crime and speculation.
If you provide storage for people's stuff and someone wants specialized storage for tulips you probably do not care whether the tulips are worth anything or useful. You rent them the space to store their tulips if you can make money that way.
And tulips are not worthless... they just aren't as valuable as people thought they were, during the tulip mania.
Making money trading or storing something does not mean that something has a use-case (hence the tulips example). So the fact that people make money off other people who think Bitcoin is the best thing since sliced bread does not mean Bitcoin has any use-case or intrinsic value.
Either way, thanks for the insight and information you brought to the discussion.