How about getting a little olde tyme religion up in this piece?
It could be initiated by a noble Priest who arrives after the fortress hits a certain size, and demands a modest chapel and a couple statues in addition to the usual noble demands.
An operating Priest could
- increase overall morale
- serve as a counselor that has a chance of getting a Tantruming, Melancholy or Berserk (look out!) dwarf out of his mood
- visit, treat and lift the spirits of the wounded
- preside over memorial services which decrease the sadness associated with death
- perform some form of semi-mystical (or just highly technical) divination for their god's favored ore, gem or rock deposits
- attempt to turn undead
As the Priest gets more satisfied, he could promote to a High Priest, Bishop, Archbishop, etc. and attract more Priests to the fortress. Dwarves who have been helped out by the priest may decide to tithe, which could accelerate the process of Priest promotion. Statues, doors, altars, chairs, etc made from the god's favored materials would increase the Priest's happines level. A happy priest sends good word back to the Main Church, who might reward your dwarves with gifts and relics.
Here's an example: your fortress hits a population of 25, and a Priest of the Silver God Astlangtham shows up. Along with the normal noble demands, he demands a modest chapel be built with two statues of any type and a table/altar (from which the chapel could be defined). Your dwarves go there to tithe, pray, seek guidance if they're not feeling well, or just hang out in their time off. Places to sit would make them happier. Over time (and tithes), the happy priest gets a promotion and sends some good reports back to Astlangtham's Pope (or whatever). A caravan shows up from the holy city bearing Astlangtham's Hammer and some silver gifts, as well as a stock of standard trade goods and a promotion for their loyal priest. The relic boosts your priest's abilities and creates prestige for your fortress.
Word gets out after a while that your dwarves are good to priests, and another Priest, this time a supplicant of the Onyx God Tholdir, arrives in the next wave of immigrants.
I think this could work regardless of whether the game world actually has magic/living gods and the like. It could be fairly optional, too; a priest with his demands not met simply wouldn't send back word to attract any others, and might give up and leave your unpious dwarves after a while to try his luck at the next fortress.
I haven't waded through all of the Development plans, though, so I don't know if this is new or not, but I think it could add a lot of flavor and fun to the game.