Is most pay for Search Engine Optimization offers basically worthless?

I started a blog 1 1/2 years ago about education. With about two to three lengthy entries a week. When I google my site, I get about 2,500 'hits.' I believe it's the content that has mostly been responsible for this. I never used one of those companies that offers SEO services. I have another blog that is a photoblog. Almost no written content, nearly all photos. After 10 months, I get about 15 'google hits' and I even tried one of those SEO companies. Why are people hung up with SEO when if their site is of little interest, it doesn't really matter if it gets listed. To me it's like starting a huge advertising campaign for a lousy product. I don't see how it would help 'sell' the item. Opinions?