I respectfully disagree. By changing your password, you can either evict an attacker who has already logged in and is watching your account, or one who plans to in the future with your exposed credentials. This is important for an email account, especially if it is used as a recovery email for other accounts (like banking, etc.).
Changing your password should be the first thing you do when notified of a potential breach.
RE: 1 Billion Yahoo Accounts Compromised