Yes. Perhaps this is what SF has to go through? I'm generally not a fan of trickle-down economics, but does the city have to go through such a long stretch of prosperity for there to be enough wealth to pay for everyone? If so, advocates for UBI may need to wait a while.
Is SF unique in such a large % of the population being mentally ill or addicts?
The difference in NYC (really, mostly Manhattan) wasn't really spending although the city had financial issues as well in the 80s. It was mostly a change in attitude. What some people now decry as "Disneyfication" for example was the political will to clean up areas like 42nd Street. Rudy Giuliani was nicknamed the proctor of New York for a reason.
The city already spends a ton of money on the issue - clearly the government just isn't great at putting that cash to use. So I don't think throwing more money at the problem will help. Truthfully the answers to the problem may make the situation worse before it gets better. You should look up an article by Nick Buckley, who runs an outreach service for homeless people in Manchester UK. It's obviously a different situation than SF but it piqued my interest because it's an angle you really never hear.
but does the city have to go through such a long stretch of prosperity for there to be enough wealth to pay for everyone?
Does SF get prosperous? Serious question; I don't know how SF's taxes work. Does SF get a piece of everyone's income, such that as the people make more money the city gets more money? What actually puts more money into SF's pocket when people in SF get richer?
Is SF unique in such a large % of the population being mentally ill or addicts?