One of the easiest ways for you to rank higher than those sites would be to setup author profiles and claim yourself as the author of the original content.

I believe that this is a very good idea.  However, I am confident that it will not solve the problem.  Google is not giving strong weight to claimed authorship at this time.

Your strongest weapon is DMCA actions and to stop giving others permission to use your content.

Your site could be suffering from Panda ranking reductions as a result of your own content being wild on the web.

Some people believe that it is very important to maintain 301 redirects for a long time.

If you have mydomain.com redirecting to mynewdomain.com and remove the redirects, then any links from xyz.com that point to mydomain.com will not go to the proper destination.  All of their clickthrough traffic will be lost.  And, if you remove the 301 you are letting the flow of ranking value to chance.  Will Google forget where those links are supposed to go five years from now.  (they might not be archiving this stuff as well as you think)  How about other search engines?  Or new search engines.

I have redirected domains a few times and all of those domains still have their redirects in place.  The cost of maintaining them is usually going to be very low compared to the possible losses.

All of my redirected domains will be in place when I go to my own funeral.  And, in the "urgent" section of my business continuity plan, my heirs are instructed to protect those old domains and redirects as if they were caches of gold.

I don't know what you should do.

If this was my site I would either find a pro who knows how to redeem sin.... start working on sites in a different niche....  or....  go to Vegas and get a job as a dealer.

"Howdy Doody"

Ha ha...  I thought that Robert Fisher and I would be the only people posting here who know about "Howdy Doody".

Thanks for the laugh.