What we really need is science: double-blind controlled trials. The book 59 seconds by Richard Wiseman is an attempt in that direction, collating the scientific evidence in the field. But much more is needed. Every assertion of the self-help and personal development field requires research that results in either debunking or optimisation.
Another aspect I am cynical about is people who have been solely successful in selling self-help material, and use their own success at selling self-help material as evidence that their self-help material is of value. If we are to trust any non-scientifically-derived annecdotal self-help suggestions, surely it should be those from people who have been successful at more than just self-help and personal development?