If the content of my email is the subject of a dispute, it could strengthen my opponent's case by proving that the message actually came from me
Wait a minute, you're getting legal action against you and the first thing you worry about, and planned to use as a line of defense is "I didn't send it.. it was faked!" ?
if you're planning to say something that someone believes is 'illegal' , well, go ahead and stop signing your email - theres no disputes. Hell, in fact, get yourself a second email address and never user it. Why? so you can always spoof it, and then have the completely believable defense of "but sir, it wasn't me"
To be honest, if you're going to say something, why not have the balls and admit that "hey, I did it!" . Thats why I sign my emails. It strengthens my convictions. If you don't want to sign emails, well, stop doing it. In fact, mutt makes this very easy for you: you can automatically 'not-sign' emails to a particular address, or you can create a folder-hook to 'not-automatically-sign', or you can decide per email.
The point is, yes, it makes you more identifiable, but shouldn't you be more worried about other aspects of the legal actions rather than using an 'I didn't do it - I swear!" defense?