I'd certainly consider redirection over a 410 or 404 -- You don't want to be throwing away the credit for the inbound links, do you? (I'm asking)
None of the dead affiliate links (links that no longer exist in the redirect file) have any IBLs. So I am not worried about losing any link juice. I just think Googlebot needs to know they are 410, and I am curious to know how to 410 them based on parameter. They all have the link structure http://www.example.com/go/go.php?url=someoldparameter. Is your recommended code above valid in this case?
I will also follow your advice, and remove the robots.txt restriction. In fact, I am sitting here thinking that it *may* have had an impact on my quality score (since Panda), given that Googlebot keeps encountering 28 restricted urls (affiliate links), and 22 of them are dead. I may have a really inflated ad-to-content ratio just based on what it "thinks" the number of active affiliate links on my site are (pure speculation, but trying to get out of Panda Prison).
Nevertheless, I do want to 410 those dead parameters.