what are they worth to someone I wonder?
See:
in your opinion what is the correct offer in euros for 10 tBTC?
Approximately 0.
0!
It seems like you're missing the point: testnet coins are
never supposed to have any value!
If it has value, it becomes worthless for it's purpose.
Most people do not mine real bitcoins, nor other tokens. But desire them from the free market.
Seems the OP can't mine testnet coins, but similarly desires them from the free market?
(Still missing the point sorry)