There is no "uniqueness" in engineering, there is only a balancing of time, money, reliability, reusability and other purely mathematical concepts. If something is unique then it is often better than alternatives or worse than alternatives. Engineering can be considered a sport much easier that an art.
Art can have seperate equivelents. Like a paintng of a beautiful landscape or a painting depicting pain. Both may have the same price but both are unique. Even two portraits of the same person will be different simply because two individuals did it or how style changes with time.