There is a file tracking every single decoration, engraving, contaminant and sewn image for all items in the game world too. I don't see how coins are super more harder, especially if it just pointed to their minting year for the image rather than tracking that specific coin.
You pay the price cumulatively for each of those. Engravings need to be tracked, or else they wouldn't exist at all - the decoration is their entire existence. There's also not all that many engraved tiles outside of your fortresses, and they don't get shipped to your fort all that often, either. Coins could still exist without an image on them. And again, we still have dozens of other things that still do, and don't have the serious drawbacks associated with putting these things on coins.
In fact, if we absolutely have to keep the detail, it would be nice if every single "minting" of coins would just keep using the same image as the minting before it, up until the year change at most. Having every single stack of coins in a year have a different set of images on it is kooky. Then, they could at least have several thousand coins all pointing to the same image and year.
While reading through all these discussions about economics and the currency, I must say that I admire so many people are interested in generating an "workable" economics system from scratch.
And I agree that (and like Kohaku said), economics is a complex system depending on many other factors, and can not be discussed alone. Still, about the history of coins, I'd say that there is a reason behind why using the image of kings on them, and it's NOT crazy at all.
First of all, currency, weather it's fiat or commodity money, besides its obvious property - medium of exchange, store of value, and a unit of count. (Basics of Monetary Economics) There are more reason behind why currency should exist and can exist - it represents credibility and debts (this concept has a name - standard of deferred payment). So the image of king/queen engraved on the coinage represents his/her credibility/authority in the place where the currency been used. Also, if you are the king/queen, the coinage is NOT your asset at all, but rather it represents your debts to your people.
In one of the previous post, someone talked about how current dwarf buck being a "perfect currency". In reality it's more of a concept of "public good". Simply put, perfect currency should be worthless by itself (true value = 0), but has infinite ability to add as many 0's on it (face value = any number). And it can be shared to everyone without compromising its usability. So why coins are invented in the first place can be answered.
Since, gold, silver or more often the alloy of both, are essentially worthless in it's "true value" using as metal (they are too heavy and too soft at the same time), but the face value of these metals are flexible because they are used as luxuries. And contrary to general believes, they are not actually "rare". but rather their easy accessibility and their easy remolding make them good candidate as currency.
These facts bring us back to the topic about the nature of coinage being the representation of credibility and debts of the king/queen. Coins emerged at the same time as big empires in middle-east emerged. Coins (or round shiny medal) might be first used as tokens for gods or symbols for individuality (not necessary to nobleman only). And this tradition continued been used for thousands of years before coins are assigned to their new roles.
Than, an economic system transits itself from commodity money using usable goods like grains or animals, and becomes a centralized economy needed in a vest empire, the simple way of who produced the most commodities is the richest person doesn't work that well anymore. The serfs may know their local lords, but hardly know their emperor. And when the emperor demands his/her taxes been collected through the middle man - local lords, the serfs still only paid their lords, but part of the taxes are now belong to the higher above emperor. In a sense, the original full take of taxes (loots from the poor serfs) are been shared between the lords and central government. So in order to accommodate the "shrinking fair take", the emperor distributed his/her personal "medal" to the local lords, with "face values" which equals to the taxes given to the central government. In modern term, the emperor is now in debt to the lords, and it's guaranteed by the credibility/authority of the emperor himself. (backup by force most of the time)
Must remember that, these medals maybe very few at the beginning (as archaeology indicates), and over time, only the current emperor can hold these medals of their credibility. So a new emperor needs a new face on the medals, and often the face value varies with each other (they are not yet interchangeable). And local lords can claim these debts from the emperor when needed (during bad seasons etc.) But when an empire expanded into varies regions using varies commodity money, so does the need for mass production medals. Medals need to be standardized for convenience and also for easy distributions. And it's not surprised that early currency often equal to a certain weight of goods, and often the goods that used in varies regions as the local commodity money. And from here the emperor can simply define a certain exchange rate of taxes commodity goods with his personal medal. And local lords soon realized they can not only claim their debts from the emperor, but exchange commodity goods they don't have using these standardized medals with their neighboring lords. The coinage were born. And early on, they are limiting in large quantity exchanges used by nobleman or long distance merchandises only. The local economy was often still limited in using commodity money.
P.S The easy production of coins also create the first inflation and counterfeit. The credibility is done by the image engraved, so when the usage of coins spread into general population (at least part of it), the right of manufacturing coins is often a privilege and entrust only to the central government for a reason. (counterfeiting are punished by death) Still, when the general demands for more currency, the quickest way is to remold these coins into more medals but with less weight individually without changing its face value. But this sometimes creates inflation (not always), hence the "real face value" was often much less. For this reason, there is the need for engraving the year when the coin being produced. A coin produced a decade ago with the same face value as today may not have the same "real face value" in the current market.