Autoblog plugins are so you can add additional products and new products in your niche.
As far as link building goes it depends :
if you have one site - then you should be building links to main page, categories, articles, reviews and direct to the main product sales area.
if you have many sites like me - then I do the above but only the active sites - and less on the sites that aren't selling or their niche is not as trendy.
As far as content same thing - I buy more content for hot sites than cold sites - If I had one site then I would be adding alot of content at this time -- as with this Google change we are not sure how long it will last -- I don't expect it will stay forever otherwise their rankings will be just target / walmart / amazon / homedepot and no-one else and that's not what people are looking for -- they want value / they want to know the product is quality and to be sold -- which is what we do in IM basically.
If your site has been penalized then I would get stuck into Social Media and get traffic that way and keep adding content - and wait it out - don't get frustrated it's just part of business.
My traffic has traditionally been 100% seo and nothing else - but now I am using Social Media more as I have bought some bots and testing them all out....... Just about everything in this post has been talked about in the thread already .. cheers.