When a mobile device is connected it's generally because I want to change the tracks on the device (its storage is only enough for half my library at a time). At the moment it seems the only way to change the selected files is to go into Edit > Preferences > Devices > Auto-Sync Settings, which is a bit of a drag. I noticed that you can right-click on the device name in the navigator pane and at least jump to the main device settings box, but this isn't quite so intuitive.
As there's already a link to the device in the library navigator, why not add a button there that allows you to jump straight to Auto-Sync Settings from there. So you would have two buttons altogether: One for 'Synchronise' and one for 'Open Auto-Sync Settings.'
On the subject of buttons, while a device is syncing there doesn't appear to be a button for 'Pause Sync' - today I had to leave the house while my phone was in the middle of a major sync, and the only option I had was to rip the device off the USB cable, causing an error in MB and leaving me unsure as to what happens next time it connects.