I'll likely never buy a flagship, given that moving from $100 - $250 - $400 dollars has made it clear that there are significant diminishing returns. That and, the sonic signature of headphones varies so much, you may well WANT to steer clear of high-end products for a better sounding lower end product.
My HD595s, while somewhat thin and certainly not perfect, are still maybe 70-80% of the HE-400s to my ears. The 400s just add some bass and texture that can't be touched by them. In all honesty, the O2/ODAC (vs hi-fi laptop sound) basically made the HD-595s sound even better (albeit with more fatiguing mids and treble), while the 400s mainly got the blackness and extra power they needed to sound their best (while the extra bass is somewhat fatiguing on some music).
I take the same attitude into regular speakers - right now I'd rather have a $250 dollar receiver, 40 inch TV, and Andrew Jones Pioneer set up (~$1,000) than a $10,000 dollar rig with state of the art equipment. 80-90% of the performance for a fraction of the price. I do, after all, want to have some sort of environmental conscious and not suck the grid dry just to watch a movie!
That said, as soon as Hifi Man or Sennheiser release another tantilizing $2-$400 dollar product, I am probably screwed. Every couple of years I get the 'itch' to 'switch'.