I voted for Cutpurse assuming they were all just crafty names.
....Cutpurse is seriously OP - and besides. Who would be stupid enough to upgrade a shop weapon? Besides a clueless newb, I don't see why anyone would waste 1,500 electrum on a weapon that does nothing.
The dirk doesn't need a buff, and neither does longsword/gavel/longbow. If they got buffs, they would qualify as 'good' weapons, like Eternity, etc.
These are non-rare store-bought items: They aren't supposed to be the best. There's nothing that is great about them: if you want the good stuff, go out and grind your ass off for it.
Don't ruin the balance of the game by petitioning a buff for something that is so easily achievable, and has no need for a buff. Four damage a turn, for only a coupla quantum?
Two things in life you should never do.
Upgrade the dirk, or drive drunk.