I work as a developer and here is my suggestion to help eliminate spam content. Robots don't turn pages, so by splitting the join into 2 or maor pages with a captcha on each section requires manual imput of membership information. When splitting the join pages is is also a good idea to allow your admins tot move around members information on which page to display membership information that is being requested
Most spam is done by websites asking for name first, then email, ect.
Well by asking for other information first then the name later screws up the normal spammer because they have the usual data that websites ask for first.
Making a changes in join forms save admins thousands of hours editing the sites for spam.