If the question is to divide Sweezy's work into (a) things he thought were true when he wrote them, (b) things he thought were useful for the Party or the Movement even though he didn't think they were necessarily true, and (c) things he thought were false and not useful for the Party or the Movement but that he still needed to say either because of Party Discipline or because it would be good for movement solidarity... that's a very hard question indeed. It is, however, a question that must be asked once one boasts that one's knowledge of technical points of economics has been sharpened and refined by contact with the thought of J.V. Stalin.
I think that the _Theory of Capitalist Development_ (1942) is mostly what Sweezy thought. He's still convinced enough and bold enough to argue that after World War II ends those nations that wind up in the socialist camp will develop much more rapidly and successfully than those that wind up in the capitalist camp.
But even in _TCD_ there are some passages that I, at least, find it hard to believe that Sweezy believed them. For example, on p. 191 there is Sweezy's dismissal of Marx's "The monopoly of capital becomes a fetter upon the mode of production.... Centralization of the means of production and socialization of labor at lat reach a point where they become incompatible with their capitalist integument.... The knell of private property sounds. The expropriators are expropriated" as "not so much a prediction as a vivid description of a tendency." Sweezy cannot say, under Party discipline as he is, that there is a jot or tittle of the Apocalypse of St. Karl of Trier that is wrong, but he can redefine Marx's prediction as a mere tendency that can be overwhelmed for centuries if not millennia by counter-tendencies that somehow Marx doesn't find space to talk about.
Nevertheless, _TCD_ is valuable both as an explication and updating of Marx and as the record of the intellectual position a very smart man takes up as he tries to wrestle with the world under the assumption that the Apocalypse of St. Karl of Trier is gospel.
I think _TCD_ is the most valuable of Sweezy's books. Later on, for example in Sweezy's 1953 essay collection, _The Present as History_, it is easier to see the Party hack. For example, consider claims that the "political leadership in the Soviet Union is acting as the agent of the working class.... [T]he working class is the ruling class in the Soviet Union," or that there is "more genuine democracy in the economic and social spheres in the Soviet Union than anywhere else in the world." These simply cannot be taken seriously as attempted descriptions and analyses of the state of the Soviet Union in the late 1940s and early 1950s by anybody who has made any attempt to inform themselves. They are party-line bilge.
_Monopoly Capital_ I find harder to classify. There is no longer a serious Party to be a hack for, no longer a Stalin for a stooge to follow. There is a bait-and-switch on foreign policy going on in the book: one one page the Communist Bloc is peaceful and subject to brutal attack by the likes of Dean Acheson who is "organiz[ing] counterrevolutions in Eastern Europe" (never mind that Acheson was a believer in containment, not rollback; hell Dulles was a believer in containment, not rollback, save when he wanted to appear otherwise for domestic political purpose); on another page we have "the revolutionary peoples have achieved a series of historic victories... Vietnam, China, Korea, Cuba, and Algeria.... It is no longer mere rhetoric to speak of a world revolution: the term describes... the dominant characteristic of the historical epoch."
There are statements in _MC_ about the U.S. domestic economy in the mid-1960s that are extremely hard to credit as attempts at analysis. To argue in the mid-1960s boom that "capitalism's basic law of motion, temporarily thwarted [during World War II] soon resumed its sway. Unemployment kept steadily upward, and the character of the new technologies of the postwar period sharply accentuated the disadvantages of unskilled and semi-skilled workers.... By the end of the 1950s the real state of affairs could no longer be concealed: it was impossible to continue to believe in the existence of a meliorative trend..." Such passages as this are much more easily classified as "things it would be helpful for the Movement to believe" rather than "conclusions I have reached through serious analysis." It leads to the conclusion that the Cold War has been generated by the U.S. power elite in order to temporarily solve the system's accumulation crisis, which is a comforting thought for the Movement to hold on to but not a serious analysis. The tone of the Heilbroner-Sweezy exchange in _TNYRoB_ led me to up my estimate of how much of _MC_ was meant to comfort the Movement rather than be serious analysis.
More interesting (and I think much more valuable) in _MC_ is the neo-Galbraithian neo-Veblenesque critique of consumer society: capitalism's problem is not that it is less productive than socialism but that its productivity is directed toward useless, counterproductive, and happiness-destroying ends. This critique does, I think, have a lot of truth in it, and I have always found it quite valuable. It does, however, lead me to places I do not want to go: "One need not have a specific idea of a reasonably constructed automobile, a well planned neighborhood, a beautiful musical composition, to recognize that the model changes that are incessantly imposed upon us, the slums that surround us, and the rock-and-roll that blares at us exemplify a pattern of utilization of human and material resources which is inimical to human welfare...."
As for Sweezy's other and later writings.... I always found anything cowritten with Magdoff to be worth reading.... I always found anything cowritten with Huberman to be not worth reading.... I always wondered how much of the stuff about the revolutionary economic and political potential of third-world socialism was meant to be taken as serious analysis, and how much just to keep up the spirits of the Movement by telling them earnestly that somewhere socialismwas advancing and utopia was being constructed.