But it is consistent with human nature: when we’re invited to a dinner party, we take wine or flowers, rather than transferring the equivalent amount to the host’s bank account.

No … it is consistent with social mores.

Moreover, when you make a present of jewellery to someone, for all you know their appreciation of the diamond earrings is as much, if not more, to do with its market, as its aesthetic and/or psychoemotional, value.

You are projecting too much here.