As a younger millennial, I have 4 basses and 1 guitar. All of my instruments are of high quality and exactly what I'm looking for. One was a birthday gift from my parents when I was in college. The others I had to work for or shrewdly trade up to acquire.
I don't need anything more than what I have. I don't have the disposable income to buy a multi-thousand dollar (or older vintage) guitar whenever. I'd rather max out my Roth IRA every year now so that I can actually retire in 35-40 years. Compound interest works in the stock market, not usually with investing in basses.