I really enjoyed reading your post. Visualization is indeed a powerful tool. When I was preparing for my very first job interview, one of my friends shared "visualization technique" to help me lessen the anxiety. It was different from just preparing for a typical job interview scenario but I'd imagine myself being the situation then roll around my eyes to see people's facial expressions, office ambience, etc. This simple exercise really helped me during the real interview and I've been doing it ever since. It's not about predicting or foreseeing what is going to happen but I would say it is more like a imagination drill of a real situation so you can be calm and confident during important moments.
I have never suffered from anxiety when I had to speak in front of people, but I can totally see how the visualization can help greatly.
As about what it is and what it is not. I think it can be both. It all comes down to the reason why you opt for doing it.