i have a business selling specialty socks that i, and my family knit ourselves.
i built a website for selling these socks to people who recognize the inherent comfort and value of such socks.

one day, i accidentally mail 500 socks to a registered buyer on the website.
the socks, unlike gold, are not a 'precious metal', and are not considered a 'currency' by any nation on the planet.
yet they do have a value to my family and i, as it took thread to make, and an investment of our time.
.. therefore, i go ahead and verify that the buyer did indeed receive the amount of socks in question,
and cordially request that the buyer help resolve this mistake amicably.
to which, they become hostile, citing 'finders-keepers'.

i'm not a legal expert,
but i've seen stupider cases on judge judy.
i believe i can sue, since, the original buyer acknowledged the mistake, and kept the product regardless.
to think otherwise is stupidly naive.

...
...

also, the argument that bitcoins are worth nothing is by its nature, flawed,
as, like knitting socks,
there are electrical costs, and an investment of time, required to mine a single bitcoin.
it is this inherent value, that you would be potentially suing for.
..
you would essentially be saying 'pay me the amount in electricity that it would cost to mine another 512 bitcoins, and compensate me for my time', or give back the coins.