You are right. 1) Put redirect to main site. 2) Make sure multiple websites dont have the same content. 3) Reduce the keyword density to 6-10. 4) Start link building... 5) Submit a review to google.... This is important.. You will reap gains...
With 301 redirects, what happens if the main page ranks #1. Do all of the domains that are redirecting to the main page then dominate the SERP's or does Google just look at the target page?
Google will "see" only one URL. The 301 response tells the SE's that a page has been permanently moved from one URL to another.