First, I would like to point out that everyone is affected by psychology and no one is capable of predicting exactly how it will affect him. You need not have a strong belief that there will be an improvement, in order to be affected by placebo, and there are more psychological effects than placebo.
Now, I don't have a decent rig so my own FLAC/mp3 experiences don't mean jack, however, I would like to submit a few links to old head-fi threads in order to show the power of psychology.
http://www6.head-fi.org/forums/showthread.php?t=133964
Guy claims to hear difference between lossless and WAV. But I don't think anyone would encourage him to encode everything in WAV so he's happier.
http://www6.head-fi.org/forums/showthread.php?t=63803
Guy #2 says that LAME aps is noticably worse than iPod and that he can't stand to listen to his music for long and that LAME aps destroys the enjoyment of the music.
http://www6.head-fi.org/forums/showthread.php?t=66150
Same guy as before executes a blind test between LAME aps and WAV. He is unable to tell the difference. He is too stubborn to fully admit that he is unable to tell the difference, and after much hard listening, concludes that there is something more satisfying about the WAV files than the LAME files, even if it is very subtle and cannot be determined by blind test. He later finds out he labeled his files wrong and that the ones he was claiming to be more satisfying were the mp3s. In reality the difference in satisfaction came from knowing one was uncompressed and the other was compressed, and not from actual difference in quality to his ears.
Now, the point of this is not to say that LAME is as good as WAV, or that no one can tell the difference, or that people who encode their music in FLAC are weak-minded (since I encode in FLAC myself), but rather to show that the reliability of people's ears isn't much better than the reliability of eyewitness reports.