All of the music on the iTS is at 256kb/s anyway. The relatively tiny jump from 256 to 320AAC would only be a psychological/academic difference for so many people. It's unfortunate that Apple has this against them, even though 256AAC is as good as 320 MP3 on Spotify, and to boot consumes less data.
Would be a plus for Spotify with their bitrate selection (96?, 192, 320). I tried using AM as much as I could today. Ended up using 250MB, which would equate to around 192kb/s assuming I estimated right on streaming time.
Btw, Spotify's OS X is the worst. And the iOS app is drudgery. IMHO, of course.