Why do you put the word value in quotes? I assume, from the rest of your post, that you are referring distinctly to economic value. But even then, the question is too general, too broad. For Paul McCartney or Santana, music has great economic value, they've made millions, or billions in the case of McCartney, through their music.
I would think that every composer finds their music personally valuable, because if they don't they'd simply stop writing. If you're referring to some distant future social/artistic/intellectual value (as Bach's music has achieved) of course nobody alive today can answer that question. People living 200 years from now will answer that question for us if they care enough to study the music of our century.
Since, as you wrote, you don't need to make a living with your music, I wonder why you're concerned with the economic value of music. I would think the personal, artistic and social value would be sufficient and gratifying enough if you have other means to pay the bills.
Some composers make a living scoring soundtracks, as I did. I made a substantial living with my work. But I got tired of doing soundtrack music after 12 years, the intellectual and artistic rewards were not as great as the financial rewards and because I made some smart and lucky investments, I was able to back away from scoring and focus on music that has more personal value to me.
Some composers aren't very good at music composition whether they make millions or whether they don't make a penny off their works. Some composers are superb at what they do regardless of how little or how much money they make. Charles Ives was a gifted and accomplished composer and he sold insurance for a living.
Values are both highly personal and highly subjective. Money and material wealth can be measured in numbers, but values can only be measured by the contentment, happiness, integrity and self-control those lived values do or do not bring to one's experience.
