Hey all - We haven't analyzed every track in the spotify catalog (yet), but we have matched most of them up to songs. This will allow you to get the audio_summary for a given spotify ID even if we don't have the analysis for it yet by returning the audio_summary of a matching song.
You can get the audio summary for the song associated with the track with the following query:
http://developer.echonest.com/api/v4/song/profile?api_key=YOUR_API_KEY&format=json&track_id=spotify-WW:track:50s4irexIfK8IoaLESWWhg&bucket=audio_summary
Hope this helps
Paul