Frankly, i would suggest a simple thing. Do a Google search and tell me how many blogspot blogs come up? Take any competitive keyword and do that. You don’t find blogspot in the top 10 and even if you do, it will be in lesser then 2% cases.
So first I would suggest to change from blogspot to a cms which supports seo. Then think of doing seo. WordPress is known for its seo abilities. So naturally you will receive more success with WordPress.
The reason you are receiving such a huge social traffic and less search engine traffic is because of blogspot. Disclaimer all this is a personal opinion