24 bit is definitely no placebo effect.. It is always frustrating to have to down sample to 16 bit.. When you hear such drastic difference.. But it does also matter what music.. But especially with ambient music I hear a difference.. If I buy an digital flac album I would easily choose the 24 bit if there was a choice.
Many blind tests regarding 16 vs 24 bit have proved that peopled can´t hear a difference. In any case, when it comes to CD anything has to go down to 16 bit anyway. To hear a difference especially (!) in ambient music is a huge myth for me. When it come to classical music with a lot (!) of dynamics there is a reason for this higher bit/sample rate rate, but when when it comes to Ambient I don´t know any music in this genre using the full dynamic making it worth at all to for the additional headroom nor a higher sampling rate.
Are people really be able to hear a difference between 192kbit and 320kbit mp3?
But OK, it´s usual that those believers feel better if they can say they feel have the tools or special gear (the price for the additional investment in those cases needs an explanation too) or rendering options. I´m pretty sure, if I would offer 2 unnamed files for a blind testing concerning this issue, those people would avoid to be part of that test.