Not sure how customizable vBulletin is? but what about limiting access to certain sections until 'x' amount of thanks/posts is reached? I've seen other forums where people are limited to certain sections until criteria are met.
ie: 2 'thanks' before you can post in off-topic, 10 before you can create threads in that section....

That way users are 'eased' into the forums.. they can start by posting in troubleshooting sections first, and responding in certain other discussions, then as they contribute more and learn there way around the forum different options are opened up....