Daniel, thanks for the article. However, I do find certain points to be controversial. 
 
First of all, it seems that you are referring to coaching as to a process of making the most of the player's potential and helping him become a professional. Meanwhile, many adults treat chess as a hobby, so they pay for the fun and the opportunity to talk about the game with a master. Similarly, when you work out, play tennis or go swimming, you pay a lot of money while not expecting to become a pro. Right? I mean, different people have different goals. 
 
Secondly, "ridiculous prices". Most GM friends of mine charge $20-$100/hour. This is less than a decent lawyer/consultant/golf or tennis coach is making. In fact, a fitness instructor with a murky background and a fake diploma is likely to charge about as much as GM. Hence, I don't think that people are overpaying for chess lessons or being exploited. Of course, there are some freaks and charlatans, but the same can be said of any industry. 
 
Thirdly, most people could use guidance and an outsider's view on their training process. Also, they need someone to help them during tournaments, both chesswise and psychologically. Furthermore, not all of us are disciplined and educated enough to create professional training plans for ourselves and to follow them. I absolutely agree with you that coaching is not a philosophers' stone that allows a mediocre player to become a GM right away. However, ceteris paribus, a person who has access to coaching is more likely to become a strong player than someone who doesn't. This has been scientifically proven. It's not only about the direct benefits, but also about commitment: if you are ready to invest your money into something, then you are more passionate about it, and your sense of responsibility is higher. 
 
Do you agree?

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Very well said, Peter. Very convincing. I took about 10 lessons from an american GM for 85$ per hour, it was a lot of money, i do not know how much rating points it gave me but it was interesting and fun for sure.

If you are a natural attacking talent like Tal, you should not be bombarded with advice about how you should play in a more reserved and strategic manner, you should be left to do your own thing. Let your talent shine. 
 
I recall Nigel saying in one of his books that most of his students want to play like Tal, even if they have a totally different natural style and level of talent...

As somebody who took lessons for several titled players. I really feel that the only real good advise I got was to play slow games not blitz. I think it is crazy to believe that somebody can teach you how to think. If you did all the things they say. It would take a hour or more to make a move. If I had to guess how a GM got to be a GM. I would say through the thing they say you should do to improve and good hard work.