I'd say with that kind of collection you're far better off with specialist insurance anyway as they;re likely to agree a value and will know to take into account any rarity. Standard home insuirance only really covers the simplest options and they're more likely to argue with you over minor differences making a huge difference in value - not the thing you want to worry about in the event of a big claim.
I have the two watches that are over my home insurance single item limit itemised and then up the values to market value every year when I renew.. For the half dozen that are well under the limit I just keep record of purchase and photos of condition and make sure the overall house contents claims limit will cover them.