Well it first starts with quality content. Make sure its fresh and unique and add it often, the more you add the better it looks, BUT quality over quantity. How about getting into social media. Your 4 blogs are related to 2 niches there for you could make 2 twitter account 1 for each niche. Start following people that are interested in you niche and just keep following about 50 per day. once you start getting a bunch following you back you then post your links to your content you add.
You can also do the same with Facebook fan pages. Get your friends liking your pages and there friends. then word of mouth will catch on and you can post summary's of your content that you post on your blog and link the rest.
Hope this helps a little