It absolutely helps - people who move to high end housing free up other, cheaper apartments (recent economic paper has clearly showed that this works, you can easily find it)

Are there any vaccines that do not have overwhelmingly positive risk/benefit ratio? (Covid and flu vaccines definitely do!)

It was true, even for young adults covid vaccine is safer than covid.

I think it's not even AI spending, but just the end of ZIRP.

Not true at all: 1) more intelligent people are happier (author of the blogpost cherrypicked 2 studies, one of which in fact showed that iq is positively correlated with hapiness. 2) IQ negatively correlates with neuroticism. 3) In fact IQ correlates positively with almost every positive facet of human experience - https://www.pnas.org/doi/10.1073/pnas.2212794120