So, there are one of two scenarios by which things will play out. If you are fans of Vbulletin and wish to see it get better, then you must in fact, buy its compeditors product. Let me tell you why. It is said that competition sharpens those whom compete. Meaning, that Vbulletin will get better by having another quality product to compete with. If we buy XenForo and it grows, Vbulletin will surely respond by getting better itself.
Likewise, if Internet Brands successfully sues XenForo creators and recieves damages, those damages will likely be based on XenForo sale revenues. If we all buy XenForo and Internet Brands recieves those monies in the form of damages, it will undoubtedly use that money to make Vbulletin a better product. By buying XenForo you are in fact, supporting Vbulletin.
Which brings us to the only logical choice. In order to defeat XenForo, we must buy it.