Yes, "Rare" can be applied to a multitude of criteria. Famous owners, seldom ordered options, including colors, limited number destinations delivered to, etc, etc. whatever you think makes your car special and more desirable than others.
That being said, I think, I own a rare car. It is a 1971 914-6 GT built by the factory. 1 of 16 made in 1971. Considering all the fake GTs out there, even 4s converted to 6s. the only one I would be happier with would be one of the 1970 models with race history or one of the 12 original 916s.