I don't think I agree. It's not the form of economic measurement that is disadvantageous for poor people, it's the fact of production for profit. Changing the form of measurement would not change the fact of exploitation, it would only disguise the real relation, making it harder to analyse, criticise and expose.
Those radical economists who are trying to reformulate GDP to include unpaid domestic work and such like are doing the poor no favours. It is very advantageous to the richer nations that they should have a scale of production that obscures the real inequalities in the world, by fixing the figures.
GDP is scientific insofar as it is a measure of the productivity of capital (which I think it is right to say that there are still many flaws in that, not least the inability to distinguish between speculative growth and real accumulation). Other proposed measures, though, only move further away from that.
(I would not say 'unfair' either. The point about capitalism is that it is at its most exploitative when it acts fairly. Fairness, justice and so on are all words to describe equal exchange. Capitalist exploitation rests upon equal exchange.)
I'm not sure that your division of necessary, ordinary, extravagant and over-extravagant is as objective as you think, either. Most goods move from the latter down the scale to the former. In the eighteenth century, a change of clothes in England would have been seen as extravagant, today, necessary.
Marx' distinction necessaries and luxuries derived not from the use- value aspects, but from the social distinction between which classes consume then. Luxury goods are ruling class consumption goods (like Yachts, artworks etc), necessary goods are working class consumption goods (cars, TVs TV dinners etc).
As for Joel Kovel and 'usufruct', Doug, 'forward to the eighteenth century!'
-- Jim heartfield