IMO it depends on what you’re buying. Exercise and training to compete in sports that I do brings me some of the most happiness I have in my life, so buying sports equipment really does improve my happiness because it lets me do what I enjoy. I enjoy astronomy and just bought my first telescope recently and it has brought me a ton of joy. OTOH I have also been pulled into the cycle of buying shit because it’s new and shiny and once it transforms from a “new thing” into just a “thing”, it loses my attention.