Members are always going to look for shortcuts and it will be time consuming for senior members to find the abusers. I do not understand that why the admin simple closes new registrations here or makes it paid or so. Members generally interested in discussions will anyway be ready to pay for this privilege. The members who do not want to invest any money for this can read the threads here without registering also. Currently, you are first inviting spammers, let them do spam and then spending time to ban them.