I for my part think solving problems should be the main goal of a particular design. If it takes its cues from things done before because they serve the best then it is the way it is meant to be. Uniqueness therefore is the icing on the cake and can not be the solely purpose of design.
I think when we talk about being "unique" in design, we're really talking about the experience & interaction of the product on the whole.
For example: Paper & Clear are very unique products. Visually they're nothing new there but the interactions & gesture both apps have are unlike anything else. When the interactions and experience is nailed down, we should then tailor our design around them.
I think that's what makes a unique design.