@Kaarme You have a point, but let me ask you this: who decides a currency's worth? The three most common metals used in coinage back in the day were gold, silver, and copper; none of those have any intrinsic value in and of themselves. Well, copper kinda does for the fact that it can be alloyed with tin to form bronze, but I digress. A long time ago, people came across gold and silver, decided they were pretty and thus valuable, which is pretty much the textbook definition of arbitrary; they were really only valuable because they were shiny and (to a pre-modern society, at least) worthless, a visual representation of "look, I have enough wealth that I can afford to buy things that serve no purpose whatsoever". Metal coinage just became a convenient way to represent wealth, since it's easier to carry around than the previous forms of money, which were often wrought in the shapes of tools like knives or spears.
If it really bugs you, though, think of it this way: the Geyl is like a Roman aureus here in the real world, while the Jewel is more akin to a penny, dime, quarter, and gold eagle in the US; sure, the aureii are
technically worth the same as the gold eagle by metal content, but from a historical point of view, they would be worth far,
far more. Assuming you could find the genuine article for sale, it probably wouldn't be that strange to see it priced at about 8,000$US (for comparison, the gold eagle is worth about 1,200$US by metal content despite its 50$ face value). They're just too valuable to spend in all but the most absurd circumstances.