I agree the Amazon sales rank tells you what is working and what is not.
My book was mentioned in an article that was front-paged on Yahoo. The author never spoke to me and didn't even represent the book all that well but the book shot up to nos. 1 and 2 on Amazon (book and Kindle) for the 4 days after the Yahoo article.
On the other hand, I've turned myself inside out to be available for radio spots and articles and the sales barely moved afterward.
So in that respect Amazon sales rank helps but other than that, not so much.