Current update 1.5.1 caravans are fine, workshops are not there yet, even in my 3000 days playthrough. The prosperity levels should be much higher, but with the current prosperity growth design, they wont rise up (cause of malus to prosperity cause of quests / issues).
I will upload my savegame, so you can check how the material prices are in all cities, i cannot gain any real levels of trade, because all prices are so close together. It might be, that the prosperity factor comes in again here, low prosperity, low demands for special goods. So i can only test this with a 100% 1.5.1 playthrough.
I also noticed that when you sell a certain good for a margin, the prices get back adjusted so quickly, you can only sell a couple units, and no more profit = no more Trade XP. I guess horses is the only real deal in leveling Trade.