The devaluation of content is real from a global point of view: thanks to key word stuffing and article spinners Google (d)evolved? ranking signals into the current model of “unique content” (is a little bit more complicated than that but…).
However if you stop for a second from evaluating SEO purely as a means to bring more traffic and you value it to enhance your product then its value hasn’t diminished at all no matter the volume of repetition on the web because the value is now to my customer on my website.
The website strategy has to evolve from just more traffic to also affect conversion. SEM and SEO have to work together but on independent aspects. View SEO indexing as a byproduct but its informative effect and enhanced customer interaction as the primary result.
If there is a place your content should be the most active is right after your SEM campaigns, in your landing pages.
Yago de Artaza Páramo