I don't recommend using Pinterest just for its stand-alone SEO value. Having an active account and using it within a larger social media strategy to reach a targeted audience will get better results for you. Then, the SEO helps build visibility, traffic and engagement for your Pinterest boards, rather than SEO visibilty to a dead end pin that doesn't translate into any kind of result for you.
It also won't help you convert that ranking into blog subscribers. There are many things that impact the success of a blog, or lack thereof. Frankly, the best tonic for a blog is great quality content (well written, on-topic, valuable/unusual or thought-provoking) that is relevant to a targeted audience, bolstered by social media sharing and the right kinds of on- and off-page organic SEO.
A great start is making sure your blog has SEO integrated the right way, and that the content is fantastic. These two articles might help you: