Sorry, I haven't read al of this, but I would like to throw in some ideas that don't seem to be in the initial post...
I would like to see doors inverted with respect to pressure plates, at present, dwarf walks over plate, door opens, dwarf walks through door. Unfortunately, door is closed, so dwarf does not try to walk through door, so never steps on plate if plate is in front of door, door never opens... I would like, door is open unless goblin steps on plate outside door, or dwarf steps on plate inside door. I can't really see a use for hooking a plate to a door without inverting the signal, unless maybe you used it to release survivors from a pit, but what happens when they step off the plate into the door way, heh, that reminds me of the original Prince of Persia, there were these sliding blade trap/door things that would, erm, well, they were messy, and that game had really good graphics too...But yeah, the option to invert all on/off signals might be nice.
mechanical workshops might be nice, adding a speed boost to the work, I can imagine a mason using a spinning cog, or a crushing device in the early shaping stage of building furniture, a mechanical drill or chisel for fine work might not fit the setting. Heavy machinery in workshops might result in some loss of material...
Conveyor belt could be useful, a dwarf would consider it to be the same square as the end-point and somehow decide to drop it in the conveyor instead of walking there. It would probably be slower than hauling, but would save dwarf-time, so maybe less than helpful for sensitive items like rawhide...
Dwarf power would be good, you could have a machine that dwarves could use to add power to a system, also I would like to see large constructions, like drawbridges, have a power requirement, and a limit to how many dwarves can use one lever, so dwarves can power small things normally form the power they can generate via a lever, but larger things would require many levers or a power supply, that kinetic battery idea would be great with this as you could prepare it ahead of time so one dwarf could quickly raise the drawbridge, but it would take time and dwarf-power to build up the power to do it again, maybe the kinetic batteries could be hooked up to a construction but add activation time that would be dependant on the power that was being applied to it. So that a drawbridge that would normally require 5 dwarves to raise, could have some batteries hooked up to it and one dwarf could raise it, but it would take longer, but not much longer if there were more dwarves working on it...
Stone traps could be multi-level, I noticed the no trap without roof entry, but if the roof was several levels up then I would like to still be able to place them, although maybe they would be more powerful but less accurate.
good idea with the levers to levers, I would particularly like to be able to turn pressure plates on and off(checks to see if that is an option on levers, phew, I didn't wast all that time on a silly pump contraption to get my one-way door working...), being able to turn off that door closing plate without fooling around with water and doors and pumps and whatever would be a boon...