I'd like to access my iPad mini file sharing via iTunes 11. However, I cannot see the iPad mini on the left hand Sidebar (View > Show Sidebar).
I also pulled out and re-inserted the USB cable a few times, quitted and restart iTunes 11 a few times.
The USB process that talks to iOS devices starts at system boot (or installation of iTunes) and not with the quit/restart of the app.
If you don't have a connection after restarting your Mac, you can download and run the iTunes installer again to see if the helper didn't get installed or started correctly.
Apple has a very nice assistant to work through common errors, so rather than my guess, you could also just follow that and be systematic about ruling out the common causes of this.
It will get you to perform both the reboot and re-install, but might solve the issue in less time. Happy troubleshooting.