Traditionally, 'off-page' is considered more potent than 'on-page' SEO. But the times they are a changin' (ok, I might be exaggerating slightly). SEO--and I say this as an SEO practitioner--has gotten a bad rap because search engines have been easy to manipulate...if 10,000 sites all link to each other, that must mean 10k inbound links!..etc. ad nauseum.
I live in the U.S. where Google is 70% of the search market, read their intro to SEO pdf, watch their YouTube videos (which can be a bit nebulous).
What you mention is what they recommend: create valuable content. In 2011, Google made over 500 changes to their algorithm, it is impossible to keep up with every little tweak. Focus on the user (and all potential users...i.e. alt text for images and such); create content that is valuable, original, and well-organized (in terms of site navigation, etc.). Use meta tags, sitemaps, keywords/phrases, and at least a modicum of social media.
I use Google Insights for Search to get keyword ideas about my topic before writing, but I also try not to just create (borderline spammy) content based on what is trending. It is a balance and on-page SEO is, in my eyes, a process of hinting--repeatedly--what your site is about, be it with microformats, navigation, keywords, or anything else...but for the love of god, don't forget things like load time and bounce rate.
If you understand, without looking up, all of what I just wrote, you will probably be disappointed with most any 3rd party SEO you hire, which is to say they are in no way required and if they make poor choices can actually negatively impact you. And if you didn't understand it all, you should look into it; you are clearly knowledgable and I come across shady practitioners all the time...there is no substitute for heart, soul, and passion.