I have a strange thought after writing my first article in my blog ,before this, i m used to hiring someone else to do it .After two week my article published ,my blog get pretty good traffic from search engine .I have checked in my analytics for top keyword ,surprisingly it came from misspell keyword .
There's always a market for misspelled keywords.. Many people have a tendency for typos. My opinion, I'd rather rank for properly spelled keywords.. the market is bigger... and yes more work is involved in ranking. I also think that have spelling errors on your site, makes your website look poor, and will turn off authentic traffic.
No they DO NOT help you improving seo ranking. Google detects if the keywords are misspelled and suggests you the right ones. So there is no point in trying to promote a website/ blog on misspelled words. Yeah, it may happen to get some traffic, but you may have a very big bounce rate. In conclusion promoting a website/ blog using misspelled words is pointless.