iTunes is better than it was ten years ago, but it's still confusing to use. The UI decisions seem random and the store is forced upon the user.
A lot of great concepts already out there.
Maintain resemblance and keep the good parts, it’s a redesign and not a new media player. I like the use of album art colours.
Customization: Visibility and reordering. If you never use search, hide it. If audiobooks is what you listen to the most, put it at the top. No more back and forth or drop downs.
Larger font size.
Place sync info with the device.
Sync to any device, I use both classic/modified iPods and Android devices (wireless sync with iSyncr). Apple is never going to support it in real life.
When it comes to UI, I think in terms of levels. At certain levels you have certain information and choices and making a choice takes you to the next level. Making clear paths to information and actions and avoiding the same function/choice at several different places.
Level 1: The main menu. Customizable, if you want to only show playlists and podcast and maybe put search on top, you can.
Level 2: Playlists, instant search results, music library etc. Lets say you pick music, the second level will show the library and provides you the controls to view and order it as you like.
Level 3: Tracks or info in an album, playlist, podcast or movie.
Level 0: The player and controls. I don't think it matters much if this is located at the top or the bottom. I put them at the bottom because I wanted it be consistent with where video controls usually are. And by doing so I also cleared a lot of the clutter away from the top.