I am using Xamarin.Android 4.10.1 with VS2012, and I cannot get any of my Android devices to show in the Xamarin.Android toolbar drop down. I have the vendor USB drivers installed, the devices are in developer mode, and USB Debugging is enabled. I can see the device in Windows explorer and transfer files to and from, so the connection to Windows is good. However no amount of Window restarts and closing and opening Visual Studio will get a device to show in the toolbar drop down.
Also I can open your Android Device Logging and select one of my devices from there to see the log messages, so Xamarin.Android can clearly see the device and communicate with it. However since they never show in the drop down I can't deploy and debug to the devices. When I hit F5 I get the "Device Unavailable" Dialog showing the selected emulatore as not running, however below that it shows my devices as available. Just as text not selectable or actionable in anyway. So again Xamarin can see the devices!