There's a famous analysis of the two stamp question attributed to R. Chaim Soloveitchik - it's cited here, albeit without any source.
Reb Chaim Soloveitchik raised the following question regarding this
scenario - there only exists two of a certain type of stamp and they
both belong to one individual. Since two of these stamps exist, they
are each worth $50. If there would only be one of them in the world,
it would be worth $100. If someone were to destroy one of the stamps,
would he be obligated to pay the owner or would we say that since
there was technically no loss of money – as the remaining stamp
increased in value – he is not obligated to pay?
Initially, Reb Chaim said that it is dependent on the question that we
mentioned earlier. If the obligation to pay, when one damages, is to
reimburse the owner for his loss, then in this case where there was no
loss one need not pay anything. However, if one is obligated to
replace an item that he damaged, and if he is unable to replace it he
must then pay for it, then in this case that finds him unable to
replace the item he should be obligated to pay for it.
Reb Chaim then said that even if the obligation of someone who damaged
is to replace the broken item, he is only obligated when there is a
loss. If there is no loss whatsoever, he is not a mazik (damager), and
would thus not be responsible. Therefore, if the remaining stamp is
worth less than the combined value of both stamps (less than $100) –
namely that the owner incurred a loss – he is considered a mazik, and
will therefore be obligated to replace the stamp at full cost.