The Longest Journey soundtrack has 36 tracks (it's the MP3 version of it - the CD version only has 30 tracks, IIRC). I don't own the GOG release of Dreamfall yet, but from what I know, its entire OST is included (22 tracks).
Great! I think the music is worth the money alone.
Hey, I might be a bit late now, but for The Longest Journey you can download the official soundtrack on the official website/forum. It went down, but they put it back up few weeks ago, since Dreamfall Chapters is happening. They have 37 tracks there, I think the GOG version has 36. For The Longest Journey: Dreamfall, the original soundtrack have 22 tracks, the CD version have the 22 track plus 4 track performed by Magnet -that music group we heard on the game singing 'Be with you'.