As I drove past "my" old house I saw that all my work was for
nothing. The new owner had ripped out the metal windows and
installed horrid white plastic ones, totally not in keeping with the
house style.

*******s!

Okay, so I may have had somewhat higher heating bills in winter, and
there was a problem with condensation in cold weather, but I didn't
care. Those metal windows would have lasted a further 100 years, and
indeed, I believe there are now double-glazed glass inserts for them.

Indeed. The availability of double glazed Crittalls is a life saver for the
millions of at-risk 1930s windows out there. That 1930s look relies so much
on those slender metal frames. To replace them with horrid plastic just
shows how some people have no appreciation for architecture whatsoever
beyond just being a cheap shelter from the elements.

Christian.