I might then take this opportunity to suggest elevators, as it is in the same theme as the other suggestions.
An elevator would be a costly thing to build, as they are very elaborate. I wouls suggest a rope/chain, a block and 2/3 mechanisms for every tile of elevator.
An elevator would allow any axb rectangle to move up and down vertically. This would be at a faster rate than walking up/down (perhaps 1-5 ticks per z-level).
An elevator, like any other mechanism, would require power. The power required would be a function of the area of the elevator and the weight on it. If the elevator does not have enough power, it does not work. It it has just enough power, it works slowly. If it has plenty of power, it works fast.
An elevator could not be built just anywhere, however. It would have to be built with a base or a ceiling. It is this base or ceiling where the power must be routed through. The elevator would not be able to travel on this level.
This would also alow for dwarf-powered elevators. It would give rise to the new skill, elevator operating. It is similar to the pump operation skill, except it allows the dwarf to operate an elevator. A more skilled elevator operator would allow the dwarf to input more power into the system, and thus make the elevator work faster. A dwarf could operate the elevator either from the base level, the ceiling level, or inside the elevator. With suitable axles, a dwarf could use a machine to generate power away from the elevator.
This could be tied in with a more realistic hauling system. Currently, the dwarves can happily haul around objects which weigh ten times as much as themselves. Elevators would allow dwarves to have to use machinery to efficiently haul heavy objects.
This could also allow for elevator stockpiles, or dumbwaiters. One of your fancier nobles might demand a dumbwaiter to bring food and drink to their dining room, so they do not have to associate with the plebs. It could also give your exploratory mining team supplies as they worked without them having to return to the main stockpiles.
Elevators could be built on, allowing for a range of uses. You could load up your trade depot safely in the bowels of you fort, before bringing it up ot the trader level. Alternatively, if you can have the caravans come down on a sufficiently large elevator. Additionally, you could build your legendary dining room on an elevator, allowing your entire fort to access it form the level thay they want to.