I have a hard time thinking of watches as investments - unless of course, you are talking about a real rarity, which of course, you will not know it is a real rarity or its appreciated value for a long time as Nanuq said.
I prefer to think of watches more along the lines of man jewelery and something to pass through the generations like a family heirloom.
Generations down the line will reap the appreciation value if there is some.