I work within the insurance industry (although not on the "personal lines" side, which this would be). I would say that the most efficient, cheapest and (likely) best way to insure watches is on a home owners or renters insurance policy.
You will need to speak to a broker in order to find the policy that fits your specific needs - you don't pay for their time - they're given a commission by the insurance company.
As a general statement, you ought to find an insurer that offers to insure your watches and jewelry on a "rider" - essentially a separate add-on policy to the main policy. By way of example, mine allows me to insure up to $30,000 in watches and jewelry without appraisal or even telling the insurance company what I have. The rider carries no deductible (I.e. I pay nothing if there's a claim) and all pieces are insured to replacement value.
A number of years ago I had a Tag Heuer Monaco stolen - I reported it and was told to go to any reputable jewelry store and get a price on replacing the piece - I'd bought the Monaco used on eBay for $1,400, but it didn't matter. As I was insured to replacement value, I received $6,000. My policy is through a global insurer called Chubb (I'm in no way affiliated with them - in fact I compete with them) - they are seen as one of the premier insurance companies for personal lines. They're more expensive but, as noted above, provide an exceptional experience in the event of a claim.