I agree entirely. Old MP3 songs sound naff cos they've been mp3'd.
I'm not
familiar with this brilliance enhancer, but I would imagine it's an aural-exciter kind of
thing, generating fake upper harmonics to replace the real ones the MP3 encoder threw
away.
If you want to improve the quality of your old MP3s, find the original
CDs, and rip again using a sensible bit rate with the AAC codec or something even
better... and lossless...

hugh
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Technical Editor, Sound On Sound