I quite agree, which is why I said, "Those who write for a living, who write for the readership, are the true professionals." This implies that those who do not write for the readership (as you described) are but amateurs, myself included.
And your example of song is spot on, for while almost everyone loves to sing (if only by themselves), there are relatively very few professional singers.
That being said, while you are right that there is no human experience that has not been written about by great writers - there being nothing new under the sun, after all - many (and perhaps most) people have unique *combinations* of experiences. As with spices for a particular dish, each experience lends a different hint of flavor, the result being a life story with a rather singular perspective.
In conclusion, then, I would advise bearing in mind Publius' maxim, "familiarity breeds contempt." If one's eye is jaded overmuch, one may well miss the true beauty of the object being viewed.