I'm wondering, would it be useful to have a plugin that penalizes messages with many spelling mistakes? This might help against all those creative ways of spelling out what the spammer wants to sell.
I don't know that anyone has worked on specifically what you are thinking of, which is an interesting idea and worth testing, I think. There are things like Tripwire that look for some outright outlandish spellings, and lots of things that look for obfuscated specific words.
Such a plugin was written by someone about a year ago -- check gmane archive of sa-users mailing list. It turned out to be not really reliable method for detecting spam.
Eugene
