But I suppose the fact that I’m willing to pay for light bulbs means that I do actually perceive that there is a shortage of light!
Maybe the problem is not the term scarcity in itself, but its scope: if you are prepared to pay for something, you would like more of it, whether or not it is scarce in the market place, so in a way it is scarce, as in “available in insufficient quantity” in your world.
But even thinking further about this: can we really say that we want more of everything we’re paying for? A test could be like this — I am buying a certain quantity of milk at, say 85p/pint. If I am offered an extra pint for free, would I take it? I think not — I simply have no use for it. So I am wondering whether your theory really holds in general.
Achieving a level playing field is certainly feasible within a more or less homogeneous domain like books (although there are some serious problems still — just like in a real market: can you compare WON with Dan Brown in a sensible way? can you compare Finnish poetry with Dutch prose?). But I think you already allude to how much more difficult it becomes when you start adding categories — films with books is just the tip of the iceberg.
I am preparing a blog post on populism, in which I will touch on quadratic voting, which is in many ways similar: it’s a money-based way of gauging preferences for public goods.
Finally, as for Piketty’s book — Amazon has of course already got the currency in which to measure the true value: the number of pages read!