This might be more of a 'technical' idea, but I think it would be really useful and the community would make some great things with it that would end up getting Spotify more publicity.
The idea would be to make an interface or API endpoint where users could pull down usage statistics for Spotify as a whole so that they can run data analysis. Creating charts and graphics based on this datal to see how the global community or a subset listens and uses Spotify would be really interesting.
In lieu of an endpoint, Spotify could provide a static page that displays certain metrics or interesting alaysis of data they choose to share with the public. Being able to see how a new single is doing, how listening trends have changed over time per genre, or to see how an artist has done over time, would be amazing.
As development evolves, this can get to a user level of granularity and could even be integrated into the Spotify app itself (which has been mentioned as part of another idea I believe).