Many people have asked the question 'is SEO really worth the time and effort' over and over again. There is true value in SEO there can not be much doubt of that, as fully optimised SEO Can put you on the front page of Google on an equal par to brands such as Walmart etc.
The main question as to if SEO can be truly worthwhile is the search engines ability to change the rules and to ban or penalise websites at a drop of the hat without any prior notice, especially Google