I accept your analysis with one caveat. These folks have subscribed to a decidedly "one-sided" Marxism, where the side of the "ought" of the worker to struggle for a higher level of social needs is virtually non-existant.
(See Michael Lebowitz, et al). Though I definitely do not find Lebowitz' arguments to be totally satisfying, to me, it is evident that a proper understanding of Capital would require that one fully accepts the one-sidedness of the text. At some point we're going to have to stop pretending as though Marx finished his project (he did not) and we'll have to work to continue it. Maybe Marx's missing book on Wage-Labour is in order... some have attempted it, though none are to my satisfaction.
I have neither the energy nor the time to elaborate. I'm currently working on a project that attempts to rectify some of these debates and problems...
I'm running out of steam on this post, but your claim that "marxist political eoncomists" assume a "value" that precedes money and the commodity trade. This is absolutely incorrect. See David McNally and Leo Panitch for authoritative refutations of this weak stance.
Good debate thus far, but I'm running out of gas. haha... The holidays have got me down, my friend.