bigboss said:
If everyone spots the difference consistently, only then it is valid. Otherwise not.
If I was at say a wine tasting (or tea tasting) with a bunch of other people, then there will be different palates/noses etc doing the testing.
Some will be more acutely aware of subtle differences - my wife has a much finer sense of smell than I have for example.
If two people don't spot the same differences, then it does not mean that differences do not exist.
Having listened a lot to subtle differences in drum sounds through a recording process, where small tweeks etc to modelling/eq etc change the sound, I was acutely aware of the differences in the drum noises that were being produced by the three different machines at the BQ, because I was listening for them.
Wheteher subtle differences are worth the extra £100/£1,000 is really up to the buyer and his/her wallet.