Sword of Spirit
Legend
Yeah, I get that you have to hand wave this away in order for it to function. However, I disagree with the bolded sentence. Value is what something is worth, not what you get it for. If you pay 10,000 for 3,000 worth of diamonds, you have overpaid by 7,000. Those diamonds don't change to be valued at 10,000. Similarly, if you are given 3,000 worth of diamonds for free, they are still worth 3,000. In my example the actual worth of the diamonds changed.
Unless I'm really missing something, there isn't any inherent correspondence of gold to diamonds. Diamonds (or anything else) are worth whatever someone is willing to pay for them.
As much as I love Planescape, I personally can't see an original boxed set being worth thousands of dollars like I've seen them listed for on ebay. But it people are actually buying at that price (and they may not be), then that really is what it is worth.
I'm not an expert in economics by any means, so you may be referring to some principle I'm not familiar with, but from what I can see, there isn't such a thing as independent value beyond what someone is willing to pay.