This seems to insightfully sweep the options pretty well.I can think of quite a few right off the top of my head.
First, pretty much anything related to inequality as long as there is a dangling carrot of social mobility: conspicuous consumption, privileged status of some white collar jobs like doctors or lawyers, even possibility to use some purely servile work that has been eliminated in the UASR.
Second, consumerism. I suppose that the FBU citizens would see the UASR lifestyle as frugal, even spartan.
Third, political apathy. Involvement in the public life is basically a civic duty in the UASR, one wouldn't probably get in trouble by avoiding it, but there will be quite some calling out and peer pressure. FBU always offers its citizens blissful ignorance as an option.
I question the "spartan" nature of life in the UASR though--obviously it depends on the social class of the FBU resident making the subjective judgement. But the question here is, what prevents the little to lose but their chains working classes from rising up--or less controversially, having such political leverage due to the implied threat they might decide to that the pressure put on the upper classes to share the wealth generously downward is strong. And strictly speaking life in the UASR will more typically be at a common per capita level but there will be some residual more or less class based surplus rich living people; these will have their eyes over their shoulders and be careful not to make waves lest the mob come and equalize them. But the large majority of wealth produced will be distributed pretty evenly per capita. This common bracket of typical outcomes will be richer, in objective terms, than the lowest classes in a parallel universe capitalist USA of the same productivity and tech level--just modestly so perhaps, but perceptibly.
Now note the very lowest classes generally cannot make a revolution all by themselves; we need to rise a little bit on the FBU scale to reach some critical level where the included classes at or below that level are large and diverse enough to pretty much do it, bearing in mind a leavening of people from all classes above--but these can be few in number and derived from individuals who set aside the basic bread and butter question of what's in it for them materially and join the revolution for other reasons.
This crucial index social level is the appropriate class to compare to the prevailing material standard of living in
red America (or the Soviet sphere, but I think most of us will agree the western hemisphere wing of the Comintern will stay broadly ahead of that of the Soviet sphere; at any rate the UASR is going to be gold plated versus other Comintern nations).
That FBU potential revolutionary index layer is going to be more well off than the bottom of the entire class distribution, but not very high up from it. Classes of people richer than that will be substantial in total number and much more so in integrated share of the national total--this is relevant to their political power to maintain the skewed order but not to the political question before the potential revolutionary masses.
Then we consider relative per capita wealth of both systems; for the UASR this is just about equal to the prevailing normal living standard in material terms. A book that introduced me to Marxist economic theory decades ago, Laws of Chaos by Farjoun and Machover, included as something of an aside data that suggested that for substantial periods of time in 20th century developed world capitalist nations, the raw split of national product between working classes (broadly, people hired as wage workers) and the whole gang of exploiting classes (more or less) was actually something like one to one; taking that as a rough guide if UASR and FBU have exactly the same productivity and working hours per worker, the FBU working classes will be half as well off as the Red Yanks.
We need to factor a number of other things of course! Part of Red American wealth is taken in non-labor time--some of this is pure recreation and as noted, a share is taken up by the social obligation to be politically active--some people will enjoy this somewhat or even a lot, others will hate it. But both segments of rest time versus harder worked proletarian FBU citizens will detract from the per capita material product to be consumed of course. If total reduction in working hours were a factor of two, that would put the typical Red Yank and FBU proletarian on the same level--materially.
Also it is insightful to note the form in which Red productivity is realized and distributed is far from identical between the systems! The FBU will be much as the western developed world of OTL, and will involve a lot of consumer goods and separate ownership of things by individuals or families, while among the Reds an increasing share of material production will go to support communal goods and services--free transport systems, parks and communal buildings with lots of services available in them citizens of a capitalist society expect to avail themselves of via consuming commodified goods in private in their homes.
Thus a clever FBU propagandist could disparage a UASR lifestyle versus FBU by focusing on what the capitalist system tends to favor producing and indexing the difference as strictly in terms of just those goods as possible; the more happy the Red Americans are with a rising share of communal stuff (they won't go for it just by ideological moralizing, or not much or enthusiastically anyway--but I do believe communal services, developed in the right way under the incentive of having to compete with the default commodified goods consumption mode of meeting needs and desires inherited from capitalism, can indeed reach a quality that seduces the masses away from commodity fetishization and can be more rational in terms of subjective satisfaction versus resources consumed and useful service work being done) the "poorer" they can be made to look by such manipulative presentation of statistics. Note too this can arise not just as a manipulative conspiracy by state or hired private propagandists (advertising firms essentially) but "naturally" and objectively when FBU statisticians honestly apply the categories they think based on their empirical experience are relevant and either come up with defective attempts to account for American collective services or just overlook their existence completely.
The trouble with this is that, especially if it is done invidiously and manipulatively rather than arise from honest confusion, is that any FBU proletarians who manage to pop over to America and hang out a while will very quickly see that in fact the services offered either for modest fees or gratis as citizen amenities are really subjectively worth quite a lot, and greatly lower the total cost of material commodities they must purchase; this subjective multiplier will thus become known among FBU masses and either the regime there takes it into account in polemics and in almanacs and so forth, or the common people learn to take these with a grain of salt and apply the multiplier themselves--and discount the credibility and good faith of their own leaders as well!
Thus, to justify the suggestion that individual working class people exposed to UASR lifestyles will judge it "spartan" by their own subjective impressions is to suggest a huge disparity of productivity in favor of the capitalists. But in fact the Red Yanks appropriate the most developed and efficient methods of capitalist production in the world, and then apply scientifically guided forms of optimizing and improvement--gross material output might grow only modestly but that would only be because of increasing "diversion" of worker time from productive labor toward politics/education/leisure time. The TL assumes that socialist and communist forms of organization developed are at least as efficient as capitalist ones and certain irrational costs of capitalism (such as the boom bust cycle, and associated misguiding of investment) are sidestepped so there is some wiggle room for laxer efficiency and still coming out ahead overall.
Since we start with the richest country in the world going Red and becoming efficiently Red rather than Stalinist, I don't think there would be any time period whatsoever when the representative and relevantly potentially revolutionary proletarian individuals of the FBU would fairly judge the Americans to be wanting in anything! If anything the Yanks would appear to be swimming in fat and luxury--maybe not to a really ostentatious degree, but rather than tsk tsking over American poverty due to their poor life choice in going Red, propaganda in the FBU probably takes a very different tack and tries to stir up resentment and contempt for the softness of American lives and impute arrogance to them (which given American tendencies to smugness and mindless assumption our ways are best, might not be hard to do at all!)--to try to make the FBU proletarian despise the Reds precisely because of their self-corruption in luxury and laziness (and also of course talk up the oppressive aspects of heavy political engagement and large time commitments given to it).
I honestly think that no matter how they slice it, FBU propagandists will be doing a fancy sabre dance with double edged sabres; their choices will be self-contradictory. It is a mess!