I certainly agree that it's speculative, but I do think the evidence is stronger than you suggest. Your counting of the strokes is consistent with my suggestion, and I think that most people, when looking at the letter, would see the referenced A-T-T-A as highlighted letters, rather than any of the others. (Everyone can look at the letters in post #17 above and reach their own judgment.)
By itself, this wouldn't mean much at all. But in light of all the other, established connections between anthrax and the hijackers (which you have enumerated well in post #36 above), I think it's suggestive. And it points to Atta as one particular terrorist involved in the anthrax mailings (which is consistent with the Prague report).