I have never 'developed links' to my sites as it can do more harm than any good. Yet, my sites gained a lot of links from many places I don't even recognize.
My sites never were the best on their niches just good enough.
"What else could one turn to that compliments this, and assists in the leverage loop to improve SEO? "
I would advise anyone to get involved in social networks where users are hanging out to bring your say in the most proficient ways.
If you don't want to advertise than the best bet is to develop a strong YouTube Channel, Facebook page, Linkedin, Twitter and slideshare accounts. Plus give away some free useful e-products. It works wonder.
Don't focus on Penguin or Panda. It doesn't worth the time.