Ah; my apologies for misreading you. But you will no doubt have noticed that we do read reports on RFF from people who spent more than they could realistically afford, and ended up selling at distress.
But it's not just Leica gear, and it's not just luxury. For the former, very often, 'users' complain that 'collectors' are 'forcing up' the price of certain cameras: S-series Nikons might be a good example. And people complain that other expensive cameras are 'not worth' the money either: Linhofs, Alpas, even Gandolfis.
I completely agree with your point that "most of the time when exchange value is disregarded for the sake of use value we're in the realm of luxury", but "most" is not "all". An M9 is in the unique position of being the only option for Leica users who want full-frame RF cameras and who may well already have many thousands invested in M-fit lenses. For some (perhaps the great majority), those lenses (and Ms) are no doubt luxuries; for others, they are not; or at least, no more so than any other camera system.
Given what I do (writing for the photo press) the only alternative to an M9 would have been to spend a lot more than the price of an M9 on switching to an SLR system that I don't like as much. Admittedly, my situation is unusual, but if I really thought my M9 were a luxury, I doubt I'd have bought it.
Cheers,
R.