Yeah a MAC Address won't save you that much. You can't permanently ban someone from your site since the internet is a free place. Everyone has access to it. When you ban someone, you don't ban the person's right to access your site, you just prevent the person from accessing your site through that IP address. There is absolutely no way to permanently ban someone from your site unless you take your site off the net.
Think about it. IP's can change. MAC Addresses can be spoofed. Cookies can be cleared. Cache can be cleared. ISP's can change.