That's a workaround, not a solution.
Seriously... expensive and relatively new Android phones can't connect via USB? What the hell is wrong with Google?
Maybe they were too busy screwing up YouTube.
I have been having exactly the same problem. In Network Preferences, it is easy to see that the computer does recognize my phone when I plug it in. And Motorola Device Manager shows in the menu bar. But Android File Transfer doesn't see the phone.