hello Walt,
you came to the right place to hear about the great capabilities of the C14. I haven't driven a Vision or any big twin tourer, so take my comments for what they are: from somebody really happy with his C14, and despite having access to many other great bikes (for work reasons) I stick with the Kawi, and my gf really likes it too.
I live in Munich, Germany, and the place, specially to the south, is full with curves and alpine passes, and taking them on with girlfriend and fully loaded bags is a pleasure. Of course I preffer to get to the hotel, ditch all the luggage, live the gf by the pool and go have fun, but getting there is definitely not an issue. It demands a bit more respect and longer braking distances, just like with any other vehicle. At low speeds it requires being used to it, since this bike fully loaded is about 1100 pounds, not exactly something you want to wrestle with. Once it's moving at anything above walking speed, the weight evaporates. Hairpins are still a challenge, but practice and it will reward you.
Regarding the tankbag, I avoid it if possible because I rarely travel in a straight line for longer than a couple hundred miles, and I need the space to move my arms. But if I do take it, it's also ok. I don't use it for a jacket though, but for my camera (a bulky DSLR) and other quickly accessible items, like a bottle of water, snacks and my documents.
I can't help you with the Kawasaki trunk which is indeed a rebranded Givi. I have a 46 lt Givi topcase which I paid peanuts for, and I'd love to have a bigger one (thinking Maxia here) but I just don't wan't to spend the $$ for it.