But so much of our own politics and ideology is about the question of allocating resources - and that does not come up, because they have essentially an infinite amount. Nobody has private property, sure, but they have as much public property as they want, and so much of it that there's almost never any drive to compete for anything - attention, sure; favor, sure; but property, or money, or things, not really.
None of which is true in the real world, of course, and so yes I agree a lot of it does not really translate to "well, what do we do here and now?". It's more "What would we do if we got there?" I guess
I often think that in the west we're actually closer to a post-scarcity society than people tend to imagine. Yes I know, that seems radical and heartless: what about the poor? Well, there sure is still a gap between rich and poor, but when you drill in to the material gap between rich and average, it starts to look less interesting. Bill Gates wears the same clothes as the average middle class person, he uses the same technology, eats the same food, he has basically the same access to mobility (private jets and yachts being a small increase in convenience but not an increase in access to locations which is what really matters), he probably takes one or two vacations a year like an ordinary person and so on.
The big differentiators between the life of a reasonably well off middle class person and a billionaire are the size/quality of their house, possibly the education of their children (but even that's a rather nuanced question given the prevalence of scholarships and state funding), and ownership of private vehicles. Maybe a bit of jewellery or art that nobody can really tell apart from much cheaper pieces unless they're for some reason an expert. And of course how they spend their time: investing and philanthropy, but let's say that's not in and of itself a big change in quality of life.
In most other respects you wouldn't know the difference and certainly the number of ways the lives of the average person differs from those at the very top have shrunk dramatically since, say, the middle ages or the 19th century.
In this worldview current trends are a predictable consequence of post-scarcity society: the rise of things like Instagram influencers, a huge class of aimless 'elites' who invariably claim to have expansive yet vague social goals, the frequency of purity spirals and so on. When your material needs are all met, your society has failed at elevating other cultures to your levels of wealth (thinking here of "bringing freedom" to Iraq/Afghanistan etc), and your society has nowhere remaining to explore physically, what is there left to do than fight over power and attention? To the extent the Culture novels explore these themes, then I guess they would interest me indeed.
There's no centralized power stricture, or even a clear definition of what counts as Culture or not. If a certain society within the Culture thinks their ideals drifted too much, they can just pack up and declare "independence".
For individual citizens, they can pretty much do anything if they can convince someone (and only if they need resources). If they think it's not really a utopia, they're free to leave and join another society.
Most of the conflicts in the book happen because, in contrast to the Federation in Star Trek, the Culture actively tries to "improve" other civilizations they have a fundamental disagreement with, and how they try to not screw it up when there are equally powerful civilizations on the other side of the ideological divide.
So while you don't get the story of how the Culture came to be, you do see it contrasted with a bunch of societies they try to improve.