They integrate with http://www.stopforumspam.com/ as well, so I've never managed a forum using their software that has had SPAM "issues".
...also their forum software comes with a amazing smartphone/mobile version already built-in and easily customized, with user agent detection.
IMO vBulletin as lost their way, esp since change of ownership (selling out). With the previous owners launching http://xenforo.com/ now VB is suing them lol.
But even the great DigitalPoint.com moved away from vB. :/ So really not many vB "Big boards" are making changes/upgrades, rather migrating to the better alternatives.
I think vB version3 was their peak! Arguably the best forum software version of all time. You'll find that vB 4 has performance issues and I mean in a addition to just the added load of features. (unless they've resolved as its been more than a year since I used vb 4)
That said if you can keep the vb3 feel with the added features it would be cool. But as it stands now, once you login, right away its "different" on every click.