[warbiscuit]

I'd argue that definition is incorrect.

To be unique, all something needs is to have a collection of properties which (taken together) are possessed by no other instance within some larger population.

Even then, it's still quite possible to have multiple unique objects within a set.

This quality of "uniqueness" can then be ranked, based on how many of those unique properties (or subsets of them) are sufficient to still make the item unique.

E.g. blue sphere among blue cubes is less unique than a red sphere among blue cubes.

So yes, "more unique" is perfectly reasonable IMHO :P