Just as it was said before, there will be a huge difference in perceived quality depending upon what type of music you're encoding. Rock, with it's purposely distorted guitar and scratchy vocals will sound much better than jazz or classical at the same given bit rate.
If you do try it, before you do re-encode everything, I would try a few differing types of music. There is some music on my machine that I would never try to reincode, others might not sound too bad.
Basicaly, there WILL be a degradation in audio quality. The difference will be that some will not be able to hear the audio loss depending upon preference in audio quality/musical tastes/quality of audio hardware.