The reason it's so difficult to talk about "value" is that there are all sorts of different things value, and to different degrees. Some people value some things more than others, which is why talking about value as absolute, rather than relative, is wrong. "Market value" is a reflection of this. When there is a discrepancy between different people's willingness and ability to pay, they trade with each other. A market is just the meeting of different people, ascribing different values to different things, and trading with each other. By looking at price at which different goods trade, we can get a rough estimate of how much people in general value various goods in terms of each other. An apple goes for so many oranges, a dragon can be traded for so many slave warriors, etc. Wealth is just the ability to pay the price for things.
Trying to ascertain wealth, though, is more difficult than it appears. You can't really be sure what you're able to purchase until you try. As he talks about the current price of something like gold isn't the price you'll get if you try to unload all your gold on the market, because the price will fall. He also seems to get into talking about "value" in an absolute way: afterall gold really isn't that useful in and of itself, etc. This all devolves into Karl Smith and Matt Yglesias offering different Westeros investment advice, trying to figure out what things will be worth in the future, as we all know "winter is coming". But this is far more complicated than it has to be.
In our world, talking about value is really difficult, because different people want different things at different times. Some people want apples, other people like oranges. But economics in Westeros, on the other hand, is really easy, at least as it concerns the Great Houses. There is only one thing that is truly of value to them, ever: The Iron Throne. That's why it's called "Game of Thrones". Lannisters, Tyrells, Targaryen's all ascribe exactly the same value to the Iron Throne: they are willing to give everything for the Iron Throne. The only factor that determines which House will acquire it therefore is their ability. Everything is just a means to this one end, so between the various combinations of assets controlled by the various Houses the one that's the most valuable is the one that gets it's owner on the Iron Throne, and keeps them there.
It's like as if there were three people, each with a different weapon, and you wanted to know which one was the most "valuable". If, like here, there's one thing they all value more than anything else, and only one person can have it, there's a really simple experiment you can do to get the result. The question "which house is the wealthiest" is just a complicated way of saying "who do you think is going to win". I can't wait to find out either.
Whenever you play the Game of Thrones, you either win or die: there is no middle ground.



