So ok, what about this variant ?
(Then let us go large ...)
1.
Valuable Wood (available on Taiga and Jungle) -->
Furniture
New SPECIAL_BUILDING_FURNITURE with 3 Levels.
Specialist Valuable Wood: Expert Lumberjack (same as normal Wood)
Specialist Furniture: Master Cabinetmaker
2.
Red Pepper (available on Hills of Prairie) -->
Spices
New SPECIAL_BUILDING_SPICES with 3 Levels.
Specialist Red Pepper: Expert Red Pepper Planter
Specialist Spices: Master Spice Trader
3.
Raw Salt (availalbe on Desert) -->
Salt
Also uses SPECIAL_BUILDING_SPICES
Specialist Raw Salt: Expert Salt Miner
Specialist Salt: also Master Spice Trader
4.
Grapes (available on Hills of Grassland and Savanna) -->
Wine
New SPECIAL_BUILDING_WINE with 3 Levels.
Specialist Grapes: Expert Grape Picker
Specialist Wine: Master Vintager
5.
Barley (available on Flatland of Grasland and Prairie) -->
Beer
New SPECIAL_BUILDING_BEER with 3 Levels.
Specialist Barley: Expert Farmer (same as for Food)
Specialist Beer: Master Brewer
6. Market would still simply unlock domestic market for normal goods.
7. New SPECIALBUILDING_TAVERN to unlock selling of alcohol in Domestic Market.
(This building might get further functionality later on.)
Comments:
With this, we would have used up all available space for new yields.
(Reserving 4 for future features like Health or Rebuild Military.)
The Terrains and Regions would be well balanced to my opinion.
(When looking at the complete list of tradable yields.)
We would introduce 10 more Yields and 5 new SpecialBuildings.
Graphics:
For Beer and Wine I already have really great buildings.
I also have good graphics for Tavern.
For the rest (Spices and Furniture), we would need to find or create some.
The Unit graphics of the Specialists are no problem, I have great graphics for all of them.