Adding a copyright notice won't stop the automatic programs from taking the content. It might make an ethical human who honestly thought it was okay to take the content think twice, but those aren't the people who generate these spam blogs.
The digital fingerprint plugins (another one at
WordPress Plugin: Digital Fingerprint — detecting content theft -- MaxPower ) are promising ways to locate stolen content, especially when they don't just post an excerpt and link back to the original post.
But they don't do anything to stop the theft in the first place.
Jay