VBulletin is a forum management software. Like most forum management software it also handles your SEO efforts to some extent. But SEO cannot be automated 100%. There are things like link building and article posting that you must do on your own. Most of the users of Vbulletin are of opinion that it does whatever they require them to do as a forum but not as a SEO tool. All you can manage is where to block out bound urls on your site. Most of the things that vbseo does is available freely on the web. Like sitemap generator. But if its a forum only you want to manage then VBseo is a good option.
Final Say:- If you need a very good forum module for your site get vbulletin it may be worth the expences but if you are looking for a seo tool vbseo its not worth the expences.