I don't really know how you quantify "number of plays" through time and attribute a "value per spin". Take John Coltrane's "Blue Train" - $10 for that album in 1957 would have given you almost 60 years of unlimited play (if you could keep the record clean!).
To a certain degree, "Buying an album" has always been a gamble. Spotify/Amazon/etc make it easier to (a) not buy albums that suck, and (b) buy more singles instead.