I agree with your statements, despite what I said about having read a few "self help" books. I opened my comment with the statement "Does the whole book change your life? No, probably never, unless you're extremely naive." So I agree, many people take them entirely wrong and put far too much faith into them.
I don't believe people need to take the books as 100% fact and execute their teachines verbatim. I've done that ZERO times. Like you said, it's mostly common sense with some interesting anecdotes, but sometimes things are presented in a way that helps self reflect a bit, and ask yourself some hard questions that you would otherwise avoid or bury.
That being said, I only read the ones I mentioned, and it was all over the period of about a year, haven't really read one since. It's not a genre I keep with or feel the need to keep up with. It was a time when I figured why not, and gave it a shot, and some of them were fun and interesting reads, regardless of being actually helpful or applicable in the real world. I think as long as you read them with the right mindset, they are harmless, but like you said, many dilute themselves when reading them and are too eagerly looking for that "silver bullet".