yes, we should follow all possibilities.
i am very appreciated for your other plugin "js insert check" that prevent spammers from register. its result is fantastic.

i just decided to use CAPTCHA if any other options can not help the situation.

i see CAPTCHA is just useful when your site is under attack by spammers that customize themselves for the site input forms. also in that case i prefer to block that IPs and create my own blacklist rather than using RBL.