The investment question
Most watches are not investments. A watch purchased at retail today will be worth less than retail tomorrow in the secondary market, because the secondary market prices out the retail margin. The exceptions are the small number of references where secondary demand consistently exceeds supply.
The Rolex sports watches, the key Patek references, the AP Royal Oak in steel: these have produced returns over the past two decades that would be competitive with most asset classes. That is documented in the auction records.
What those returns do not tell you is that the people who made them were, almost without exception, people who collected first and treated investment as a secondary consideration. They bought what they loved, studied the market seriously enough to buy correctly, and held long enough for patience to compound.
Buy what you want to own. Learn the market well enough to buy it right. Hold it. If the value appreciates, that is a good outcome. If it does not, you have owned something remarkable for years. That is also a good outcome.
CollectorGrade take
Buy watches you want to wear and are proud to own. Study the market carefully enough to buy the right references at the right prices. Hold with patience. The investment returns, where they exist, tend to accrue to people who followed this approach rather than those who treated a watch as a ticker symbol.