Okay, I've reviewed this again.
It seems that reputation CAN be spoofed in vBulletin. There's not really a central reputation center, so there's not a place where a comprehensive list could get messy. So for vBulletin we would add the wiki reputation to a new table and update the same user counters that update on regular reputation.
XenForo, on the other hand, doesn't have a reputation system similar to vBulletin. When importing vBulletin posts to XenForo, the reputation is imported if positive, and is imported as a like on the post. We can just do the same thing when importing VW3 to XenForo, and then the Likes support that's already in place would handle the rest nicely.
However, I have increased the time-to-complete to 6-hours estimated since a separate reputation system needs to be written for vBulletin installs.