Kstensland92,
The valence attribute is available on all songs as well as uploaded tracks when you get the profile with a "bucket=audio_summary" parameter. You can also use min and max valence in song/search calls like so:
http://developer.echonest.com/api/v4/song/search?api_key=API_KEY&format=json&results=10&artist=radiohead&min_valence=0.8&bucket=audio_summary&sort=valence-desc
(Note that Radiohead's highest valence song is called "Optimistic".)
The search usage is not documented yet as we've been reviewing and revising our model for valence, but that could be changing soon. Rest assured it is not going away.
To get valence for an uploaded track, call track/profile with the "bucket=audio_summary" parameter.
David