Oh, OK... I thought you guys are talking about that "visible" signature at the end of mail message (incoming or outgoing).
But, anyway... why make so big noise about that little header (invisible) inside each message ? It's not like it's adding 20 Kb to whole message file... besides, I'm not storing e-mails like they're of some sentimental value to me.... I receive them, I read them, and finaly I delete those read e-mails...
No matter is it header or signature, I think it's very important to have them... the price is too small for what you get.
Regards !