Topher - I've bought watches and parts from Europe and the UK without any problems on the receiving side. They can be tracked; they show up; they get her rather quickly by common carrier (FedEx or DHL) as compared to being sent by Royal Mail -> USPS.
As gatorcpa says, insurance generally tracks to declared value. However, at the point of payment the watch becomes yours and it might be covered against loss in transit by your homeowners policy if you have jewelry coverage. I know my policy covers my incoming watches.
US Customs duty is based on declared value and contents. It is generally paid by the carrier and then collected from you as an add-on. The shipper rarely knows the duty. It's happens at our border. FedEx happily bills you later by invoice, and I think USPS and DHL will wait for you to hand over a check to the driver.
Customs duties can be minimized by one of two paths used by many shippers/buyers: understating the total value on the commercial invoice papers ("$200 used watch"), or by incomplete declaration of contents (e.g. calling it "used timing device" rather than "18k gold, 31 jewel chronograph and bracelet") or "Gift $25". I doubt the risk is high if someone wants to fictionalize the invoice - at worst there will additional duties owed. Personally, I play it straight with declarations.
Still, the customs duty doesn't have to be very high - and can be very low. For most watches it is calculated based on a 3-part formula that allocates the declared value among the movement, case, and strap. The movement carries a fixed fee of a few dollars (e.g. $1.53) at most. The case is assessed low single digits, maybe 5% (from memory) and the strap can be 10%. So if you buy, say, an old Marine Chronometer for $4000 I would be comfortable stating that 80% of the value is in the movement, and another 15% in the case (incl. dial) and perhaps $200 or so in the strap. FedEx customs agents working on your shipment will call you to get this breakdown. Take that call! 😀 For other carriers, direct the shipper to break out the declared value explicitly as you assess the relative value of the three components.
-ez
