Excellent analysis on how much people on average spend or music. There is an amazing graph highlighting the growth of the number of iTunes Store accounts and the associated decline of average spending on music per account (from $39 in 2007 to $12 in 2012).
The latter is the big question. My experience with the major labels when I was CEO of eMusic was that they largely did not believe that music was an elastic good. They were unwilling to lower unit economics, especially for hit music, to see if more people would buy. Our experience at eMusic taught us that music is, in fact, elastic, and that lower prices lead to increased sales. If the major labels want to see the recorded music business grow again, I believe the price of music must fall.