Unlike him, I’ve been getting gibberish spam (they literally don’t make sense), including one today on a post that was 9 days old. In reply to his post, I think he linked to the wrong plugin. I’m not sure what Optional Comment Moderation does, but I do know that Auto Moderate Coments does allow you to moderate old posts after user-defined period of time (it’s very simple to change, mine is set to 10 days). Plus, the plugin developer explained its functionality very well.
I agree with Michael’s comments, especially that it’ll take some work to weed through the moderation queue. But, your visitors can interact with you with basically no additional work on their part, and you can hopefully develop a more stable readership. I’m still not using any spam plugins, just Auto Moderate Comments, and a good comment moderation word list.