If you have Well traffic forum, then I think no, Mostly popular forums don't have vbSEO. ex. DP, WHT, or others
I don't think its required to have vbseo to rank high. I have it for its other features (such as analytics tracking and etc)
Use a sitemap generator. It helps a lot - especially if you have a big forum. http://www.vbulletin.org/forum/showthread.php?t=184573 Other than this feature, I doubt vbseo can have any significant effect on rankings.
I dont have VBSeo and I am ranking quite well for my key words in google. Make sure you have a sitemap generator and an SEO Friendly skin though. I am using a free mod that makes links friendly which you can see in action at my Coventry City Forum. I don't think it is as powerful but it does the job for free rather than the high price of vbSEO.
Negative - you do not have to have VBSEO in order to rank well. The best things you can do to help your site rank well: 1. Use the free site map generator offered by vbseo. Just go to VBulletin.org and do a search for sitemap generator. 2. Edit the Meta Description in your VB forum and include as many keywords as you can, but keep it within reason. To edit your meta description, log into your VB control panel - left hand column - Vbulletin options - Vbulletin options - General Settings (it should be about the 3rd option down) and look for the Meta Description box. Put the keywords for the market you want to reach in that box. Click the save button at the bottom. 3. Change the "Powered by VBulletin" message at the top of the browser window. To change the "Powered by" message - VB control panel - Languages & Phrases - Search in Phrases - search for "powered by" - scroll down until you see "x_powered_by_vbulletin Standard Phrase" - click the edit button, Click the "copy default text" button. Then you should see {1} - Powered by VBulletin. Remove the "Powered by vbulletin" and put in a slogan for your site. Make sure your slogan contains keywords for the market you want to rank in. Do not make the "powered by" slogan and your site description the same, change them up for better ranking. When editing the powered by slogan, make sure you leave the "{1} -" in front of it. The {1} - function calls the site name. Even if you do not install the site map generator, at least change the powered by and meta description. Those are very important keywords that a lot of forum owners over look. As an example, my site holds several #1 spots on google and I do not have VBSEO installed.