It seems to me that when you define "mid-size sport tourer" clearly in your mind, you should be able to pick out a bike pretty easily, or will decide that you have to build/farkle one of your own.
Is mid-size a displacement, weight, length, horsepower or other spec? What combination means mid-sized to you?
What is a full fairing? Is it defined by the amount and cost of plastic or by the amount and placement of wind protection?
What is smooth? What is power?
How much are you willing to spend? How old or new is acceptable?
Are you looking for a "class" of bike, or to you have a purpose or plan in mind of what you want to accomplish and are looking for a bike that fits?
An last but not least, is your son looking for a new bike, or are you trying to fit him into what you want for him?
It just sounds to me that "something different" is what you want. In my mind, the Ninja 650 is a mid-size ST. Add some hard or soft luggage, or both. Windshield, seat and bars to suit, and off you go. Same with SV650/S. If a 650 is a "small, beginner bike" to you, and a C14 is full-size, then I guess the C10 is a mid-size ST.
Without knowing any more of the facts, my guess is that a few adjustments to the Ninja (seat, bars, windshield, and better tires), and some more rider training would be worth considering as an alternative to swapping bikes.