I know there have been plenty of threads about reputation and stuff, but I personally think this version would work well. That is, if vBulletin allows you to customize features. If not, this would have been a complete waste of my time . What if, you could give positive reputation to people a certain amount of times per day/week. Not too much, maybe 2/day or 5/week. There would be no negative rep, so nobody would have -100 or something like that. You could also look at who gave what people rep on people's profiles. If you see one junior member that has maybe 5 posts give all of the rep to one person, you could report it to a mod to look into that. That way people couldn't abuse the rep system by making separate accounts. Just my opinion .
Ok, why wouldn't you want negative rep, maybe keep people from going into negatives, but negative rep is like a slap on the wrist to that person.
