Indeed. A character with Improved Weapon Focus, Improved Weapon Specialization, and Improved Critical all in Rapier is a fearsome thing despite the low (1d6) base weapon damage.
What about weight and price? You give them for the base, but one needs to know how they change with the various qualities.
And how about adding a quality Heavy that just increases the damage category. It would be incompatible with Light but that's probably about all. Otherwise, how is one ever going to get into the big damage categories?