Juan, to answer your topic question (What percentage...?), I believe there's a large percentage of people that really know about sound, i.e. what sounds good and what doesn't. Most people can tell the difference between excellent and poor sound. For example, a first-time listener to a high-end system usually reacts with delight, pleasure, surprise, and appreciation.
However, because this hobby (like most hobbies) is driven by perception and experience - including the economics side of the hobby - you can conclude there's going to be a wide range of perception and experience as to what aspects of the sound are more important, especially for people like musicians. Perception and experience are as varied and unique as our fingerprints.
Nevertheless, while it may be almost impossible to create a definite standard acceptable to everyone, we can still agree on many commonalities in determining what generally sounds good as well as differences in sound quality.
With regards to the other issue you raised about personal financial capacity, all I can say is it's just a matter of choice - once again, based on perception and experience.