In my opinion, professional members make a professional forum. Of course with good moderation, the forum will be better. I dont believe that the design is part of this whole idea, its only to attract members to join it. For example look at webhostingtalk.com, the forum design is not as professional as this one( I dont like it to be honest) but that site's members make it look good. Im pretty sure that if they changed the design, most of members will vanish, because usualy they get addicted to the site by its design. A forum cannot work without good moderation no matter how professional the members are.