There is nothing in his constitutive understanding of power that insists that political action must focus itself on specifics within the co ordinates of capitalism and the state, rather I'd suggest that Foucault's rejection of such revolutionary politics steam much more from his really crap take on class and Marxism, coming as it did through a prism of Althusser. Capitalism and the state are only particular formations of power, they are disciplinary regimes no more guaranteed to contain their own excess than feudalism was, even if capitalism as a dynamic system depends on this perpetual movement of excess, of escape and capture.
i agree that Foucault's understanding of Marxism was skewed however, his own activism confirms that his system only allows for specific actions... prison reform, gay rights, the vietnamese boatman crisis.
as far as i'm aware the latter is the only time Foucault ever attempted to make an effort towards a universal politics, where the best he could come up with was the international community of the governed. which really just comes down to a very general those who speak inside of power and those who speak as included exclusions within power. i can't find a link for this anywhere unfortunately.
discipline itself cannot be resisted, and as you have said there will always be codes and structures of power.......so why bother resisting? to swap one set of codes for another? well thats all well and good, and its true one set will be better than another...but from within Foucault's system there isn't anyway of saying that. as everything is constituted by power, power becomes the only measure........ as such, there is a lack of normative grounds for distinguishing between better or worse. this is what Foucault himself referred to as his pragmatism....and its clearly part of his Nietzschean inheritance... politics, power-resistance, becomes little more than the competition of mutually constitutive forces.
here i think Badiou's idea of a universa singularity is useful, and can rescue elements of Foucault's project...but it involves a return to antagonism and contradiction which Foucault has no interest in.
Like you say the real problem isn't the impossibility of resistance breaking completely from power, the problem is that Foucault rejects the proletariat as a revolutionary agent, not surprising since his notion of the proletariat was one passed down through the Leninist orthodoxy. Likewise Foucault's rejection of dialectics should be understood within the context of a orthodox Marxism that saw history unfolding towards a nice neat ending and all conflict and contradiction would wither away into a unified organic whole. Foucault's rejection of concepts such as alienation can also be linked to this Althusserian marxism he was raised on. Althusser rejected the early Marx's writings on alienation, species being etc and rather dishonestly painted these concepts as relying on some ahistorical (humanist) essence, that should of course be rejected, infact you ape his argument with this
i can concede that... but even with alienation secured, there is nothing within Foucault that makes alienation and non-alienation good or bad, damaging or restorative (if that word isn't still too linked to organic wholeness.)
like with his work on madness, Peter Dews rightly points out that Foucault ends up in a curious position where a mentally healthy subject and a subject of madness are identical, except for the operations of power that subjectivise them in their relation. he can't condemn the process, nor can he say that madness is an authentic experience (which he wants to) as his system can't admit of authenticity.
this criticism isn't wholly unsympathetic. we could well do without authentic/inauthentic distinctions...but only if we have a standard to put in its place.
Or in other words the excess of power produces a subjectivity at odds with itself (that is as a disciplinary regime).
this is true for Marx but not for Foucault. resistance as excess is always immediately captured by power. Foucault did attempt to begin formulating a subjectivity that exceeded power's original generation... but he never got there.
]Personally I find that it's quite possible to simply swap Foucault's constitutive power for Marx's starting point of human activity or labour with very little difficulty. Capitalism is a structuring of labour that like power produces (not to mention needs) it's own excess, or in Marx's terms it's own grave diggers.
negativity allows for a form of escape from capital. but power/knowledge cannot produce that kind of agency because resistance (or excess as you say here) is still caught within power. it is a constitutive excess... one which, excessive though it is, is caught within power's orbit. it cannot escape its conditions, cannot escape its power-effects. if it could then power and resistance would be separable categories, dialectical categories. but in Foucault this is inadmissible...impossible.
further, capitalism is a total system with a central term... capital. power has no central term. there is no centre to attack or to liberate. foucault's society is the society that is fractured into agonistic competiting discourses and counter-discourse, constituted subjects reclaiming or denying their identity.... essentially its liberal fair with a multitude of voices in continually carving out a public sphere........... as he asserts quite strongly on his essay on Kant's What is Enlightenment?
also, i'm not sure that you can really talk of power having an excess and try to wed this to Marx. Captialism doesn't produce an excess in the proletariat, it produces a lack, an evacuation, a negation. isn't that the point of the proletariat? the theoretical and actual negation of the present?
as a side note, disciplinary techniques are still at work but i would fall more to the Deleuzian-Agambenian side with their talk of 'societies of control' and security.