I like the idea of a trap strength, done in a way that works as a skill vs. skill contest. Traps don't actually have skills, per se, but quality levels factor into how well it does what it does. This can be extended to as we move toward roll-your-own traps in future versions, but for now I'll describe it in terms of pre-baked traps.
The trap should have some chance to surprise the target, and a separate chance to affect the target.
Step 1: Surprise
If a creature notices that a trap is present, it can path around it or take its chances trying to get through. Good Observation skills would alert the creature to the trap's presence, and perhaps Mechanic skill would give a rough idea of how dangerous a detected trap is. Semi-intelligent and non-intelligent creatures might be good at detecting traps but not so good at deciding what to do with that information.
"Sniff... sniff... traps all the way across the hallway. Damned dwarves and their machines! Now, can I dart past them or should I just go home? I'm a lizard with an IQ of 8, decisions aren't really my strong suit."
The stealth "skill" of the trap should be based on the quality of the trap components including embedded mechanisms. Maybe the skill of the mechanic who installed the trap could play a role as well.
Step 2: Affect
Once a creature enters the trap's tile, the trap springs into action and attempts to affect the target. If the creature was truly surprised, it would be at a disadvantage to dodge/parry the trap. The attack "skill" again depends on all of the trap components, perhaps including the installation as a component.
For pre-baked traps, things can be play-balanced on a spectrum from "easily hidden" to "reliably effective when triggered." Maybe the player can explicitly spend quality points on the stealthiness and effectiveness of the trap.
Later, roll-your-own traps will involve many more components, but the same principles can apply. The only issue is deciding early on which path to take:
1. The game recognizes player-built traps and resolves things in a simple skill-vs-skill manner.
2. Creatures have a chance to observe any machinery at all (big bonus if it actively powered) and depend on AI to attempt to avoid being in the wrong place at the wrong time. This puts a premium on trap designs that spring quickly, but it should have the side-effect of keeping dwarves from getting mowed down by minecarts.