So I've been thinking, since I don't use a lot of traps due to their super over powered nature, I don't have much reason to have mechanics - Even though I build quite a lot of machines and use power for a lot of things (most of which are water). A machine built by a totally ignorant dwarf is just as effective as one built by a mechanical genius - It doesn't make any sense.
So my proposal, mechanic devices require regular maintenance, based on quality, or they may fail.
Edit: That had to be cut short because my computer decided it HAD to shut down because of some error, and gave me a couple of seconds to do whatever before it did, and then promptly stopped working. Which, honestly, is just more support for my contention that complicated devices should break.
Anyways, I imagine it working a little bit like this - the mechanics go around and access things, keeping them maintained, and the longer they go without maintenance and the lower quality the pieces, the greater the chance of them failing. Picture the fun! Collapsing windmills, malfunctioning magma levers, traps that hit friendly units or just fail, pumps that catch fire, rollercoasters that go flying off the trackes, carrying a score of people to their fiery doom in the lake... err, sorry, wrong game, but still a good example of mechanical failure (And who knows? Maybe some day...). Once it breaks, of course, the mechanics still have a chance to fix it unless its destroyed.
It would also change (In my opinion, in a good way) how mechanical systems are built, since you'd actually have to have everything accessible, which I think better fits the setting anyways. Access hallways and such. And eventually, you'd really want to replace all those crappy machines with high quality pieces from your now much more experienced mechanics.
Failure suggestions:
Powered devices:
Failure can cause device failure, or increase device power cost.
Unpowered Devices:
Failure causes it to ignore or greatly delay signals it receives. Doors, floodgates, some traps, simply don't work, or work later when you don't expect them to. Best part? You don't know which.
(eyes the magma door that failed to trigger earlier carefully...)
Triggers:
Failure causes the detector to either switch what sets it off to something else (in the case of triggered traps and motion plates), send a switch signal once, or simply not send a signal when used.