I agree that musicians should endeavor to explore all ages of music, but disagree with your assertion that criticism in art & music is a negative. I'm a musician, and I'm openly critical of all art & music for several reasons.
Some of my favourite periods in music were periods in which artists began to take an overtly critical stance on the artists before them. In the realm of music, for instance, sometimes targets for criticism were in the populist category and other times were members of the avante-garde. Post-punk wouldn't have happened were it not for those artists that came to revile "progressive" rock and criticize the necessity of writing piece after piece displaying the artist's masterbatory virtuosity. While I enjoy many styles of music & art, it's important to me to be able to take an objective view of all else, find whatever flaws I can and constructively use criticism to push my own subjective creativity. Destruction & creation are two forces that can, in turn, bring art to new heights.
Another is that criticism in some amount can help filter art & music of obvious pretention as well as allow us to recognize the unskilled charlatan from the skillful genius. I think music knowledge and criticism goes hand-in-hand. Without overt criticism, the art world would become saturated with DeviantArt-esque hangings in galleries, and without an appreciation for art through the histories we would see several artists doing numerous re-tracings of the Mona Lisa, each receiving admiration and the highest of praise.
Some artists & musicians are inclined to put "expression" on a pedestal above "talent" or "skill", and this degrades both the artist and their art. Whenever possible an artist should take great pains to work on their craft and to develop skill in order to better express their vision, as well as study the past to gather an idea of what's been done and what hasn't. Self-criticism, constructive criticism from others and an objective approach to one's art are essential to the open-minded artist.