I'll apologise upfront because I haven't had time to read the entire thread. Feel free to ignore me if I am ot or redundant.
Having said that, from my perspective, the biggest problem with modelling the economy without aids in the game is going to be accounting. You'll spend your life doing data entry if you calculate everything by hand. So, I would organise the economy around things that are already being accounted for in the game. Pretty much that means book keeping and appraisal.
At the moment there are calculations for created wealth, imported wealth and exported wealth. The created wealth is handily broken down. So you can account for held/worn objects (essentially objects owned by dwarfs). I might be tempted to issue stock for the rest of the wealth. That would be fairly easy to do with a spreadsheet and only requires that you type in all the names once. Then you can issue stock once a year, for instance, and keep a running total. Nobles can be issued more stock than others. You could then issue stock bonuses for creating an artifact, or saving the fortress from certain doom, etc.
I would not account for architecture or other things in the fortress. Instead use it as a perk. In other words, instead of rewarding a dwarf with stock, you can upgrade their living conditions. Otherwise the book keeping is going to get out of hand.
Again, to keep things simple, I would not do any accounting until profit is realised. Wealth inside the fortress is not realised wealth. The goods are still being used for whatever purpose. When you trade, you realise the wealth. You can use the difference in the exported wealth to determine the actual realised wealth. In reality, we always trade at a loss, so you could also factor that in if you want, but I'm not sure I would bother (though it would give a reason for having a good broker).
Finally, when you have calculated the realised wealth, you can pay a dividend based on the number of stocks that the dwarfs hold. I'd pay something like 5%, but really the amount is arbitrary. You can keep that owed money on the books, but I would be tempted to mint coins equal to the amount that you pay and keep it in a bank. You can then RP dwarfs spending their money to get exclusive use of artifacts, or to upgrade their quarters, or to demand certain foods being stockpiled.
If you want to get super tricky, you can even track inheritance in the event of death -- with or without a tax.
Actually, this sounds like fun... I may have to try it...
This sounds fun too! Micromanagement is an issue for sure, but then again, isn't DF all about micromanagement? After all, I just finished building individualized gold tombs complete with statues commemorating great feats and memorial slabs for 45 dwarves...
From what you describe, it sounds like an 'Adventurers Corporation" from 17th-19th century England, France, and the Netherlands. A group of merchant-adventurers would band together, pool funds, and establish a trading or production facility in a foreign location. Each would have a share of the profits according to their investment and of course participation. There were a number of very famous of these... East India Tea Company, Hudson Bay Company, Jamestown, Plymouth...
I'd have a bit of a different spin on it, but just my thoughts... what you propose sounds fun!
The always trading at a loss is an interesting point. I think that is part of DF to reflect the merchant's grand ability at bargaining. That said, as an economist, it is rather mercantilist thinking (aka, trade equates with one side winning and one side losing). I like to think of it as the cost with transferring goods ("transaction cost" using economics jargon) going to a merchant (aka, it costs them 20% to 40% to move goods from one place to another and they need to add a margin for that). Under that notion, trading is transferring some goods (aka, 1000 lead goblets) for something more useful (aka, 10 bags of gypsum powder) plus a cost for trading. This totally ignores the concept of specialization, which is why trade is such a good thing, but I will offer an elf in sacrifice to the economics gods for forgiveness. Therefore, trading actually means losing profit. The value of exports minus value of imports equals transaction cost, which is a reduction in profit. I guess this can make sense in that perhaps the DF has to order 'essential' goods from the mountainhome in order to survive. In doing so, they have to pay a lot!
Wealth then would be some grouping of the other reported numbers minus the initial wealth (what was brought with at embarking) and minus the transaction cost. I agree architecture shouldn't count, nor probably furniture. Non-portable and totally cant be easily buried in the backyard. That leaves weapons, armor and garb, other objects, displayed, held/worn. I have no idea what displayed is. Held/worn is stuff being used to generate a profit. Does weapons or armor/garb get double counted with held/worn? If not, maybe one of those two could be used as the 'profit' good? Instead of tobacco like Jamestown as the 'profit' good, the DF makes battleaxes? As a result, profit is realized when the value of battleaxes exceeds transaction costs and initial investment...
One could totally have fun with shares too, especially with children. Oldest gets inheritance while younger ones must be indentured servants or drafted into the military? Hmmm... many, many possibilities...