Regarding the question of a "structuralist" Poulantzian view of the state vs. an instrumentalist, "Milibandian" view of the state, I think framing things in those terms is very much an Anglo-American perspective.
In German debates, the Miliband view is almost entirely disregarded, and the question is framed in terms of Paschukanis vs. Poulantzas, or more acurrately these days, a synthesis of Paschukanis and Poulantzas.
With Paschukanis you have the question posed, as raised here by Carrol, of **why** does class rule in capitalist society split off so that it is mediated economically by the commodity form and politically by the state form.
Poulantzians and Post-Structuralists tend to disregard the question of social form entirely (I think Foucault stated quite expressly he was even uninterested in the state as such, and more interested in government), spending more time elucidating the **how** rather than the **why**,
But this counterposition of a Hegel-Marx-Paschukanis-Frankfurt School lineage on the state versus a Spinoza-Marx-Althusser-Poulantzas lineage is more and more breaking down, and the more interesting state and legal theorists, like Sonja Buckel and Joachim Hirsch, are attempting to reconcile the two.