There is a new BBC radio program on the "Business of Genetic Ancestry" While it is true that without seeing your DNA (or even asking your name) I can tell you that you are a descendant of Charlemagne etc., I still feel there is great value in testing your DNA for genetic genealogy purposes, especially autosomal DNA.
I agree that the deep ancestral stories given by the main DNA testing companies are vague to the point of being meaningless, but I believe that the value on the information that can be gleaned on more recent generations is much greater. And the data is being kept which means that in the future we may be able to learn more from tests done on people now.
Honestly, I hope as many people test as possible and it doesn't matter much to me what their reasons are for testing. Many people who have tested for me have done so mainly because I asked them to. I have followed genetic genealogy testing since it began. It is still a new tool. I remember when we thought that 12 marker Y-DNA matches were very significant or smaller than 5 cM autosomal was likely significant. We don't believe this now, because we have more data that has allowed us to refine our understanding of what the matches may mean. I am sure in the future we will further refine our understanding and change our positions on lots of aspects of genetic genealogy testing. Without lost of testers this will not happen as easily, if at all.
It was not discussed in the program but the value of a test has gone up and the price has gone down. When I first tested my own autosomal DNA I paid 4 times the current price and the databases were less than a third the current size.
You can listen to the BBC radio program here http://www.bbc.co.uk/programmes/b05vy4kb
There is also an article on the content of the radio program at http://www.theguardian.com/science/commentisfree/2015/may/24/business-genetic-ancestry-charlemagne-adam-rutherford