As far as upgradable workshops goes, I don't think it's as cut and dried as just increasing the rate of production. If workshops are using more raw goods as inputs, and producing more manufactured goods as outputs, it will end up
increasing the price of the input (because the quantity of that item in the town/world will be lower), and it will
decrease the price of the output (because the quantity of that item in the town/world will be higher), which might actually lower your overall profits.
Here's a test to show what I mean:
I started a new game and used the console to give myself every brewery in the world (23 in all), and let the game run for awhile to see where my profits levelled out. With 23 workshops, I was earning roughly 2900g/day (+/- 500).
Once the profits stablized, I switched the least profitable half of the breweries to another production and sold them back to the notables, so I was left with 12 breweries. After waiting a few months for the quantity of goods to stablize, my profits had shot up to ~4100g/day, so I was earning over 1k
higher profits with
half the workshops.
I then exited the game and went into the workshop xml file and doubled the production rate of breweries so that each one turned 16 grain into 16 beer per day, and reloaded the save where I owned 12 breweries. My profits jumped substantially for a few weeks, but then dropped way back down to slightly
below what they were when I owned 23 workshops, to about 2500g/day.
I then adjusted the brewery variables again so that so that each one turned 8 grain into 16 beer per day (so a 1:2 ratio of inputs/outputs), and reloaded the save where I owned 12 breweries. My profits again jumped, but then slowly fell until they stablized to about 3500g/day, which is
lower than 12 workshops turning 8 grain into 8 beer.
So the takeaway from this is that there is a sweetspot for global production rate of goods by workshops, and just raising the input/output numbers for upgrades might not result in better profits. The best outcome here was 12 breweries total in the world turning 8 grain into 8 beer per day.