The only purchases I regret are random cheaper ones, like Monoprice Modern Retros, and about half a dozen sub-20$ KZ's. It adds up to maybe 150$ though, which is the same as taking a hit on a single pair of prosumer bluetooth headphones. Overall, not bad.
I've settled in nicely with a 6XX and some s12s as my best headphone and IEM. I've got side-grades for different use-cases, but with the kind of deals you can get for speakers these days, for the the same price as some LCD's or ZMF's, I'd rather invest in stereo equipment, which I believe has a higher ceiling for fidelity than cans.