I regret mostly not giving my purchases enough thought in the early years. Sometimes I would re-buy things after selling them, which is a fantastic way to waste your trust fund, if you've got one.
I also needed to look at the bigger picture. Say, I probably should've bought the TF10 and it woulda lasted for 3 years, instead of buying a pair of $100 phones each year because I assumed I have $100 as a reasonable, sane budget cap. They add up pretty fast!
If I have to be specific, everything I bought from Audio-Technica I regretted. They are far cheaper than Bose, but to me they're worth a lot less.
Amps are a nice thought, but I tend to feel that anything I would buy that's expensive enough, will sound nice on the most feeble of sources. That's part of their duty for costing so much
Better than just having them sitting in a drawer collecting dust.
