Well , got hold of a SID from my dealer earlier today and have just finished having a listen.
FWIW - CDP is an Arcam CD37.
Pre-recorded discs - no noticeable difference in sound at all.
Burned discs - possibly some minor improvements across the frequency range.

Not sure if there is any particular reason that there should be a difference with lossy ( 320 kbps ) music - maybe someone will be able to give a rational explanation.
Worth £20 ? - probably not to me. If I only listened to burned discs then possibly.
Not sure if any of this helps or just muddys the waters a bit more. Yes my observations are purely subjective as at the moment I have neither the time or the inclination to do a bouble blind test

Cheers.
David