hard choice but of the things on there. i feel dacs are a waste of money. and bitrates above 320kbps mp3 is also useless. i never notice a difference between 320 and flac.
amps make a difference if headphones need them to be driven popular. but past the fiio e9 i feel amps are also a waste of money. i understand tube amps give a bit of a distortion like sound a kin to vinyl. not really a good difference but there is a difference. i personally wouldn't pay when you could recreate the same sound with computer software.
room treatments regarding speakers do make a difference. i notice when something goes in front of my speakers they generally sound wonky. but i don't feel it is really noticeable unless you have a really expensive set of speakers.
now price. yes i do believe price makes a difference. generally the higher the price the better the quality. the difference might not be worth the improvement but it is there. there is always the few exceptions where you can find something offering really good sound for cheaper then the competition that it can compete with items much more expensive (shure srh series, audio technica ath m50, grado sr60/80/ms1. but i still feel generally the more expensive the better.
now some people do not buy into better sound quality and actually prefer a colored sound. in that case finding very expensive colored headphones is not an easy task. and you can get really good colored that to them is better then the much more expensive options. but do to the dynamics of audio and audio science we know it doesn't faithfully reproduce the recording realistically and is not better. but every individual is different and some will prefer inaccurate sound signatures.
anyways that's my take on this matter.