What is Rare? Sure, some things are rare -- not to say many things are. ;-) But for sure there are some horological rarities that seems to be invisible:
Massive Solid Gold Watches Are! Especially the ones that are very special and bound to a specific period or era -- for example very iconic 70s or 80s watches.
Why? Because the more special they appear the higher the chance they go out of style at some point or another in time. When you have a usual / classic watch in the common sense, then it would be used and appreciated during all eras, no matter from which direction the wind blows. Yes, but lets have a look at the specialities, the characteristic kids of their time; what happens to watches that are out of style but have a high material value -- of course, these are the first in line at the smelter. So, these solid gold watches were made in smallest quantities compared to their steel siblings and get lost to a huge portion to the smelter -- thats why these are rare and become rarer.
So, this is why we think the collector of solid and massive gold watches not only collects the most interesting and most beautiful watches, but also the most endangered ones -- he is basically the preserver of a threatened species.