Personally, I think it depends on what area of watch collecting you are in.
From my limited perspective, the areas of vintage watch collecting that are "booming" are: 1. stainless steel, 2. Chronos and diver (sports or tool watches in general), 3. certain middle-high range Swiss makes like Rolex, Omega etc., and 4. large 37mm + vintage pieces. Quality is always important (unpolished case, original and clean dial, original movement etc.). These are the watches that younger (i.e. millennial) collectors seems to be interested in. Although, at 30, I'm not really attracted to those sports watches.
Before getting interested in Longines and Omega (clearly at the wrong time), I was a big, and still am, Hamilton collector. My primary focus was gold-filled, tank, tonneau, and cushion-shaped watches from the 1920s to the early 1950s. Those watches were really popular in the 80s and 90s, but have fallen out of popularity (and value) since then. Another area that was huge in watch collecting from the 80s to the early 2000s was American-made, high-grade pocket watches, specifically railroad grade watches from Ball, Hamilton, Illinois, Elgin, Waltham etc. Those watches were more expensive 20 years ago than they are today. It's actually a pretty good time to buy a high-grade pocket watch for a good price.
Click to expand...