Hi vinchenz,
Value isn't just one thing. There's
replacement value for insurance purposes (for which you should obtain an appraisal), there's
resale value (which is lower), and there's
sentimental value, which only you can determine.
(There's also
historic value but these are not historically significant pearls.)
If you are considering selling the pearls, I suggest you look at what similar items have sold for at auction. Not what they are listed for, but what they have actually sold for. You can easily do a search on eBay for
sold, pre-owned Mikimoto pearl necklaces.
For example:
https://www.ebay.com/sch/i.html?_fr...Condition=3000&rt=nc&LH_Sold=1&LH_TitleDesc=0
Pearls do not tend to hold their value on resale, because of how easily they are affected by skin oils, cosmetics, pollution, as well as poor storage conditions. This is because they are so soft.
That said, Mikimoto pearls will tend to hold value better then generic pearls, because of the desirability of the brand name. It would also help if you had paperwork for the pearls, as clasps can be replaced and anything can be placed in any box.