Hi, you're wrong. From what I read it's true he can upgrade to member rank by purchasing cooper membership here https://bitcointalk.org/index.php?action=credit;promote (Paid in BTC) He doesn't mean the "highest rank" but "higher rank"
I wouldn't call it an upgrade, more like a privilege.
The user maintains the rank of a Newbie (assuming he/ she hasn't ranked up yet), with Member addons. He or she still won't be able to join signature campaigns.