The New in The New Music immediately suggests an element of the unfamiliar, unusual, strange, foreign, or alien. Sometimes this may indicate wholly novel materials, but mostly the novelty is in the deployment or arrangement of the materials (John Cage/N.O. Brown once again: syntax is the arrangement of the army). Sometimes a rage for the new (Morse Peckham: Man's rage for chaos; biology, behavior, and the arts) is a form of criticism, a more-or-less explicit expression of dissatisfaction with existing states of affairs. Sometimes this is an ethical judgment, other times this is simply fulfilling a need for variety. We all have some need for variety: in music, in food, in clothing, in landscapes, in the arrangement of furniture in our living rooms. And, most likely, we have some need to manage a balance between variety and stability, between the unexpected and the predictable. (In his later years, Cage always wore the same kind of clothes, French worker's denim, so that he needn't think anymore about them.) Someone once told me that variety reminds us that we're alive, by inserting events into our lives, while repetition reminds us that we're still alive, and measures our lives by creating intervals between events. Thus a passion for the new is not necessarily a discounting of the old, familiar, but can be a way of renewing our experience of the old, through ever-new contexts.
(N.B.: X is done, and without hiding it behind an "e" (exile, extreme, exotic), nor grabbing onto the musician's inevitable xylophone.)