Almost everything in audio is over-priced and then there are diminishing returns. How I weigh that will always depend on my capital. If I were super-rich, I doubt that I would accord any of it much weight. But, realistically, very good is good enough. I try to make that my rule.
The mid-priced headphones (e.g., K70x, DT880, SR225i, HE400, HD6x0) are all very good. I know I wouldn't be happy with anything less good. I've tested the most common expensive headphones except expensive Grados and Stax, and the only one that impresses me is HD800. I think it's 2-2.5 times as good as HD600, so its value is $800-1000 not $1500. For any of those prices, I'd rather own several mid-priced headphones that are very good with different genres and instruments.