Are they collection cats?
Then they are worth money for the costumes.
If they are regular boxes then the traits hidden on any of these boxes would be old and outdated. I would not keep them for the sake of breeding. I would only keep them for the sake of sentiment or if you thought any of them were pretty for pets.
I would not assume that they would sell. Unless - as I said above - they are Collection cats with costumes, in which case they are worth a pretty penny.