Workshops (rugs/paintings) dont increase room value, only furniture does that.
Here is an idea from me:
Make a basic human template. A civ with traders and guilds, and copy it 5 times.
Asian (japanese/chinese) with katanas, kimonos, sake, dojos, martial arts, and japanese language file. Nobles called shogun and daymio etc. Their kidnappers and thieves could be called ninjas.
Western (britons/french) with halberds and longbows, steel, muskets and cannons. Nobles named king and dukes etc.
Southerners (greek/roman empire) with gladius and legionnaires. Togas and sandals. Latin language files. Nobles are ceasar and praefects and the senate.
Arabs (ottoman/persian) with kaftans, turbans and scimitars. Mass mud brick manufacturing, great doctors. Nobles called Sultan and grand vezir.
Amerindian (atztek/maya/inca) with bows and spears and macautlis. Shamanism and blood magic (human sacrifices and all that) and nobles called high priest and god king.
Other options: African tribes. Germanic/barbarians. Vikings. Mongolian hordes. Egyptians.
The basic idea: The human race is the same, but the weapons, graphics and noble names change, and each different culture gets 2-5 unique workshops. Its not that much extra work, and with the gui you can mix them up as you like.
Play as Westerners with early Amerindian Invaders, buy your steel from the Roman Legion to defend agains late Arabic invaders while you get visits by japanese ninjas (lvl15 thieves, like kobolds but more dangerous)
Or just enable one of them, the one you like most.
It would be a neat community project as well, because smaller parts can be done by different people. If you have good historical knowledge or always wanted to do 1-2 things for a specific mod like vikings or japanese, that would be the perfect oppurtunity. Once I finish the basic workshops that they would all share, it would be simple to split them into different cultures by a few small additions.