What exactly is Skagit casting and how does it relate to underhand casting, Spey casting and overhead casting?
There is no pat answer to the above question. It all depends on whom you talk to. A lot of the questions your asking have been covered here, some in great detail, many times before. As I've said several times the archives will answer a lot if not most of your questions. Every good writer that I've ever heard of does one hell of a lot of research so if your really interested in any of this you will be starting with the archives.
The guys visiting and posting here will go to just about any lengths to help a "newbie" but they don't like to have their time wasted by constantly repeating info that is only a click away. Every subject and question you've brought up so far can be answered by a trip to the archives.
As to the promotion of spey casting I think everyone here is doing their best to promote the art, sport, science, addiction, whatever, of spey casting. As to articles in mags about spey casting, I know of one MAJOR national publication that had an article benificial to new spey casters in a special edition and didn't publish because for whatever reason they couldn't sell enough advertising. The mainstream fly fishing mags are just that, "mainstream". Why spend $5.00 for a mag with one (maybe) spey casting article when you can read spey all day, every day right here thanks to Dana, Sean, and several other people that are generous with their time.
I'm averaging about 2 years in a "hobby" before I'm burned out.
If the above is true you just as well bag it now because unless you spend some serious money for some one on one lessons with someone with the ability of a "jedi master" you will most likely not have mastered spey casting before your burnt out. In reality that is where a great deal of the "little used" rods on e-bay come from. Peace and Love from the left bank.