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.
Really not what I meant. I mean you don't chase after happiness with purchases. You know how like people chase after happiness with alcohol, drugs, etc. These things won't make you happy, you have to find happiness in life at a more fundamental level.