Powerstones and Intrinsic Value

[Bruno]

If you're talking about depreciation and local price differences, you're already off into a far more complex economic model than that particular rule was ever written for.

It's written for an economic model where there's a price list in a rule book where Persian rugs cost $250, and the GM's notes might say "Persian rugs cost 1/5th list cost in Iran" and "Persian rugs cost 2x list cost in Canada". That would make the intrinsic value of the Persian rug 250$, because that's what it says on the price list.

Yes, this is a brutally simplified and rather unrealistic economic model. If you're not an economist or economics-minded, this is an abstraction of convenience that makes things work with a relatively simple rule (the binomial equation involved aside).

If you prefer a more economics-minded approach to things, I suggest not using "value" at all, as it's a purely ephemeral concept. Come up with something based on physical properties - perhaps going right back to the original "Must be an opal, reserve capacity is based on weight in carats".