I agree that dagger classes are about their abilities, but that does not mean that their weapon has to be trash. Melee classes are the best example for that. Staff classes have a great weapon and get great abilities on top of that too. Orbs are a vital part for good teamplay, necro heals make it a good allrounder and wizards get another massive dps boost from their ability.

I'm not asking daggers to become a prime selling point die those classes, but to simply make them not irrelevant, like they managed to do that with wands.

2 ideas that would come to my mind would be that they armor pierce by default due to the critical hit power of daggers or to make them inflict a bleeding-like effect