You know, it doesn't pay to look too much into the economics of the Federation and how some people own chateaus and vineyards and others live in trailers in a supposedly, completely equalitarian society. But here goes:
I mean the idea that it is "post scarcity" is nice but what does that mean? Well, you can have a society where no-one goes hungry, is homeless or lacks medical care or education. In fact, we could probably do that now if we chose to. Equally, there probably isn't the equivalent of the hyper rich who acquire massive wealth. Think of a society closer to modern Scandinavian countries where there are people who are wealthier than most but the gap between rich and poor is nowhere near as extreme as say, the US.
As far as access to substances are concerned, presumably people have the equivalent of a guaranteed income from the state that they can spend as they see fit. If they choose to spend it getting high that's their decision. After all. Picard makes wine so alcohol is legal. Given free medical care and better treatment facilities perhaps addiction is less of an issue, and even now, some countries provide addicts with free heroin as it's cheaper than dealing with the crime and medical issues that are caused by people having to source it illegally. Here in the UK registered alcoholics on state benefits can receive extra money to allow for their need for alcohol (as, unlike other substances, you can die from withdrawal of alcohol) and heroin addicts receive free methadone as a substitute. None of these things cause most of the population to become addicts, they just provide a better life for those who would have gone down that path anyway and reduce the crime that can go alongside addiction and impact on the rest of society.
Presumably, the Federation ensures that the needs of its citizenry are met. If some people choose to drop out of society, then that is their choice so long as they don't bother others. Raffi doesn't seem to be causing any problems for other people. Their society also allows people to "drop back in" much more easily. After all, by the end of the show's run she's the first officer of a starship (granted they are probably a bit short-handed after the events of Frontier Day). Perhaps there is also some sort of “wealth tax” that limits the amount that can be passed onto heirs or allows people to become relatively wealthy but beyond a certain limit, kicks in to ensure no-one becomes too powerful. Picard can inherit a vineyard and chateau, but he may need to provide a proportion of its “profit” or whatever passes for it, to the state. In the UK in the 1960s and 70 for example, there was a 95% income tax bracket for the highest earners (See George Harrison’s “Mr Taxman” on Revolver), as well as high death duties on those passing on inherited wealth, which is why all those stately homes are now mostly owned by the National Trust rather than old families.
Well this ran on longer than expected. Anyway, just my thoughts on a subject the show's creators understandably gloss over.