yes the basic vbulletin skin will most likely not bring many new members and nothing else is there to intise(sp) the users into registering. I would suggest finding a design firm,person, or company to give you a layout with you can not make one yourself. I would also like to know your forums main angle or topic such as your forum right now doesnt presents its topic clearly and i as a user would not know if i wanted to register cause i dont know whats its about.
So those are some of things i caught right off the bat and i wish you luck with your forums