Looked up the tranquil, I like the idea of it, but feel for DF lobotomies would be more appropriate. Butchers the brain, causing the ability to learn to drop drastically, but makes the dwarf completely unable to spaz out when Terrance the kitten stumbles into some lava. Lobotomizing miscreants would also be much cheaper than giving them drugs or performing some magic ritual. Any surgeon could do this, no magic needed. Of course, a chance of failing and killing the dwarf, or making them a vegetable would add further risk. This would most likely be a cheap and relatively easy solution to the handful of dwarves in every fort that are never happy and always taking it out on everyone else.
What I was hoping for is some kind of end-game content, though. Something akin to a social version of adamantine. Basically, Soma from Brave New World. To qoute Huxley "All the advantages of Christianity and alcohol; none of their defects.". Some kind of potion, drink, or food that bestows calmness on the imbiber (probably by means of imparting a short lasting syndrome on them). Naturally, it would have to be consumed on a regular basis, and would probabaly be very difficult to manufacture on a large scale, and would have the effect of slowing the dwarves down, both mentally and physically. Withdrawl would be a total nightmare. However it works, it would probabaly be absolutely vital to maintaining a large, functional dwarven population center. As things are, the mountainhomes should be nothing more than a steaming magma soaked crater, the victim of one thousand temper tantrums, all because someones pet cat died and they lashed out at someones pet dog, and so forth.