Imo it's mostly its our mood/health that affects Audio. If I'm in a happy mood my gear sounds awesome, if I'm tired and fatigued, my mind switches into analytical mode and sub conciously picks out all the flaws and emphasises them, If I have the Flu all the treble seems to be non existent, all these circumstances make me start questioning my Gear. The funny thing is, the next day the same album I played yesterday could sound a lot better, my gear certainly hasn't changed, I'm just picking out and focusing the best parts of the Audio instead.
I've even gone as far as questioning the quality of the electricity, funny that.
Of course, gear such as the Speakers/headphones/Amps often do play a huge role in the SQ - but this is mostly subjective as we all hear things differently. Unfortunately for our wallets we tend to pick out similar priced gear to match, ie, spending a fortune on wires - where tests have been done between coat hangers and there was no difference in SQ, and Now in light of this Thread, changing Dacs have been found to not make a difference between a $2 and a $2000 model.
We've all been there. One day you could be hearing the worst in the music you listen to, grab the credit card and make a regrettable expensive impulse buy hoping it will all change, and by the time the gear arrives, you're in a happy mood, everything sounds awesome, it must be the gear, so we come to these forums and boast about it, a little while later, our minds become used to the "placebo change" and so it all starts again. Question is, how many of us actually plug back in our old gear and do blind tests? I admit, most the time I don't. Knowing that you've spent a fortune for something that doesn't sound any different can be an insult to oneself.
Similar to the article above, A well known Youtube channel stating it's snake oil after numerous blind tests were conducted. Linustechtips - http://www.youtube.com/watch?v=UZ_kxbuMt5Y&t=32m10s