[Kromm]

You might want to look at Every One's a Critical in GURPS Dungeon Fantasy Denizens: Swashbucklers (p. 26). Its rationale is as important as its stats, so it may or may not work "as is" in all genres. Given its prerequisites, it's likely fine in a genre where people are routinely launching Deceptive Attacks that give -5, -10, or more to enemy defenses.

I consider the soft cap on the price of critical-hit enhancements to be 40 points. For that, you can be invisible and just stab defenseless people all the time. Anything less good, with less noncombat utility, should cost quite a bit less. I'd put the floor at 8-10 points.