No-one writes a bad demo this is far too subjective to be of any use and should be avoided.About the audio files, I think good AND bad demos are important to understand how easy/hard is to use a lib,).
I don't think audio should be posted on a public (unbiased) wiki. Our ears are biased and we are full of in-built prejudices. If you love Spitfire then you will most likely think a demo for a Spitfire library is "good" compared to someone who hates Spitfire who will naturally think the demo is "bad". A wiki should be a place for facts not opinions.