Does SPF protect the domain found in the visible "From:" or 5322.From address field?

No. SPF checks are performed against the domain specified in the email's "MAIL FROM" address, which is also known as the "Return-Path" or "5321.MailFrom" address. The "MAIL FROM" address is used by the email server to determine where to send bounce messages, so it is an important part of the email delivery process.