I bite the bullet and did the IPB - VB - Xenforo convertion and it has worked out fine there. However when I moved the site from a testing url to the main one - all the pages are showing up as 404 Page Not Found.
Note that ImpEx doesn't preserve group permissions during an import but XenForo does. So your users will have no permissions when they are imported to vB and that will carry over to XenForo. That includes Follow message moderation rules. You should review the permissions of all imported groups. Or you can simply delete the imported groups which will move all of those users into the default Registered group which already has appropriate permissions.