There is perk Fast Hands in utility tree.
It remove AP cost from weapon swap. Problem is that after using weapon you can no swap it(I think).
There are also Executioner perk in offensive tree that increase dmg to body as HP drop beneath 50%.
Actually to use Dagger effectively you need fairly experienced hero.
The best I find is to use him with other one armed with club.
The first guy stun. Then guy with dagger come.
Perks Executioner, Fast Adaptation(increase chance hit after miss), Push the Advantage(increase chance for crit and hit against stunned targets) also high melee skill.
Lightly armed(so high max fatigue) but with shield(additional defence).
Then you can puncture enemy to death and get fresh new armour.
The universal armour stealer.
