Have you blocked categories and tags from indexing? otherwise duplicate content will make your blog disliked by google. Use seo plugin to deindex categories, Tags, Archives, Pagination. I have around 2.5K posts on an old domain and all long tail KWS with low competitions, after around 3 months I see visitors gradually increasing very slowly. I have talk with some splog (spam blog) experts, they have some tools to make thousands ( 30K to 70K) of posts on all most all types of longtail kws at a time, and wait at least 3 months to start seeing visitors. I have almost all posts indexed and 100+ kws within first 10 average positions, according to G-webmaster tools. But overall I am not much satisfied with MB, in love and hate feeling

, but if it has the ability to post on at least 10-15 web 2.0s it would be an excellent seo tool, my opinion.
MB is not yet so much efficient to rewrite quality articles from search engine scraped content. Moreover, (most likely) its default paragraphs shuffling and mixing makes illegible articles. Main problem is it does not follow sub headings and mixes paras under subheadings. Sometime footer author intro comes to the first paragraphs. first paragraph not always does not carry the keyword a vital point for search engine to understand the context. MB works good with quality content so choosing a niche having good quality content is essential so selection of niche has some effect.
I hope in coming days these points will be corrected by developers. He is working hard to make it efficient and respond to any problem if let him to know.