Artists have done some amazing things with collage:
Cut-and-pasted paper and printed paper, charcoal, ink, and chalk on colored paper on board. Picasso 1913.
Picasso did used a lot of musical themes in his collages - guitars and sheet music. Picasso used wires and glass, and all kinds of paper.
Mixed Media Collage With Silver Leaf
(I couldn't find a year on this piece - but she is a current artist)
So far, I have been fairly happy with my results. But my collages are a lot more simple than this, working more with patterns and colors than layers. I hope to post some collaged mini cards in my etsy shop soon.