mmm, school chairs. bent tubular pot metal with spot-welds, and wood laminates riveted on...
So, consider the modern world. Post industrial countries have negative population growth. Industrialized countries have slowing population growth. Wars are drastically diminishing in scale when compared to 100 years ago.
Traditional drivers are population growth, and conquest. Also, the desire for goods that are not available in your local market.
Planned obsolescence may not be an exclusively modern phenomenon, but it is pretty close.
I'm all for things getting broken in fires or tantrums or invasion or general combat spillover -- more masterwork defacement is always fun. but I think the economy can find better sources than this. Isn't this the point of the dynamic world? Isn't this the point of tracking the production of goods in every town through all of worldgen?
I imagine part of the economy will be a greater demand for things that your culture can not produce, or that are not available in your biome. Greater value might be placed on things not available in any of the biomes your entire civ has access to
I imagine another part may be driven by population growth -- if towns are expanding nearby, they may need textiles or tools. You might get a contract to quarry blocks, or cut timber in bulk. Maybe to produce bulk lots of charcoal, or even salt.
I imagine that conflict may be a driver. Armor and weapons and foodstuffs could be in demand when nearby civs are at war.
A rich neighbor may want luxury goods, a neighbor with a bad cropp year might pay a high price for seeds. When the mountain homes or one of their protectorates have a need, they may demand tribute or assistance from you. They may even demand soldiers, or skilled laborers.
As your fortress its self becomes more wealthy, residents may begin to value more luxury goods... Prices of rooms may fluctuate based on demand and based on means, such that immigrants and unskilled workers are priced out of quality accommodations, and have to resort to the barracks.
Also, I expect that the same random "Item A is valued at 60% next visit, and Item B is valued at 115%" kinds of things will serve as a placeholder for all of the above, until such time as it is actually implemented.
Replacing broken tables and worn out toy mini forges... This just isn't interesting.