Firstly, I would revamp the whole forum. Change the style, banner and layout and before you do it browse around gaming/wii forums to see what others prefer. Start to ask people if they think this looks good etc. Once you have a very good forum then start working on the content of it. I am not sure if you already do it but do reviews about the latest Wii games and things coming out, that sort of stuff.
A lot of the time, first impressions are everything so if you forums looks really appealing and attractive then they will think good thoughts. So after you have made it look nice and improved the content then start to do as much advertising as possible. Leave a link in your sig on every forum you are a member of, take advantage of services forums offer and request things like post packages as much as possible.
Another very useful thing is post exchanges. They are the quickest and easiest way to get fast posts that make your forum look active. You should do as many of these as you can because the more you do, the more posts you get and the more active your forum will look. If a forum looks attractive, the content is good and it is active then it should make the guests join up. If doing a post exchange though I would make sure you do it with people who know a fair share of gaming because you don't want posts in all your off topic forums all the time.
You should also start to affiliate with some other Wii based forums or websites, it is getting your forums name around to others who also enjoy playing the Wii. I saw that someone recommended you get a .com or .net domain, that would be a massive boost for your forum and if you can't afford one keep looking out because on some forums they have competitions where you can win a free domain, we have had some here.
Anyway, I hope this helps you and I really hope you can get your forum back on its feet. Don't forget though, every forum has its ups and downs in activity. ~smile~
Note: You can find some really good advice and tips on our blog too -
http://forumpromotion.net/blog/
