The value in historic artifacts lies largely in the information they convey about ancient times. Replaceable things contain mostly mutual information with their replacements, so if you got a complete ancient bowl set, say, that would be a lot less informative than the same number of bowls from different sets, except on the matter of the existence of such sets.

Uniqueness/rarity of such things doesn't increase total value, but it does increase marginal value (the value to gain or lose one more item).