The audio examples are really fascinating. (via).
When composers wrote for these instruments they sometimes loved them and sometimes chafed at their limitations, but in any case they wrote for those sounds, that touch, those bells and whistles. From old instruments, performers on modern pianos can get important insights into the sound image that Mozart, Schubert, et al., were aiming for. But music from the 18th and 19th centuries doesn’t just sound different now than on the original instruments; some of it can’t even be played as written on modern pianos.