As a GM, I really enjoy the roleplaying aspect of commerce. Relationships are established, friends and enemies made. Merchants have families and secondary business partners while players are always trying to hawk some pretty strange, even wild merchandise, which can lead to meeting some wild and strange NPC's from various professions, guilds and even races.
Tracking coins is something as a player I
really enjoy. A griffon farm on Ciros will have a small hoard of gold coins, but a village in Haestra will have 8-15 buildings, including an inn/tavern and simple Earth Mound of Illoura: A regular center of civilization. PC's will have a hard time breaking a gold coin. In fact, the merchant will have to cut coins and rely on a scale for a fair deal. A quartered gp is 25bp each...22.5bp if the PC's don't demand the merchant clean the cutting blade
And don't forget the charge to test strange coins purity. The simplest test is shave two small pieces off the coin and anneal the with a hammer. If you can meld the two pieces back into one easily, it's fairly pure. A level 4 potion can make Coiners Acid in my game, which determines purity by the color the acid turns.
This means some serious book keeping, which I don't mind, but most players...well, it's easier to just "magically" make change than go through all the paper work (players are lazy!). It is a game after all. I'm just some weirdo who enjoys minutia.
Any form of long distance travel across Emer/Jamain/Kulthea is down right expensive. I just started a new group and they have yet to travel beyond a days march from their home town, but when they do they will "discover" Reandor and its feudal kingdoms and see their first ship, AND they know nothing of the flows or how they might impede travel...I digress (I'm good at it!).
I always wanted a highly detailed of flows. For the longest I have used them as plot devices and random encounters. People who travel into flows without proper protection are usually never seen again. Entire villages may disappear in a dimensional rift. So they remain the greatest barrier to travel, but admittedly rarely reach sea level, and were they are known to, no one goes without a navigator or their own compass.