Firstly - Masterpiece weapons would all have a decent damage dice. Something like 1d12 minimum or whatever.
Secondly - they all would have nice combat benefits depending on the weapon.
Of course Masterpiece weapons would be extremely hard to wield successfully, so they would require a feat to use (there's no non-proficiency penalties, you either can use it or not). There would also be feat chains or maybe even trees for improving benefits or gaining new ones.
Alternatives involve making homebrew Martial Disciplines for each such "Exotic++" weapon.