I'd love this as well - although I do rate some of my collection, I don't rate it all, especially not until I've seen it once or twice.  It would be incredibly useful to have a feature that would set/update any review value that I haven't set myself.

In fact, a slightly more generic feature that would work would be to add some method of setting the "user" things in the database (rating, watched, basically anything in the "Personal Information" tab) via the new Command Line feature.  I could use this to set things based on other sources that I found interesting.

Thanks
-Jeff