Kris,
A board is a board, it cannot be compared with a website like Facebook in any way. Facebook is personal, account on a board isn't. It's for fun, solving of problems and everything else that cannot be done via Facebook.
Can you solve a technical problem on Facebook? Maybe. But there's a big possibility that you don't have someone who'd know the solution in your contacts. You may ask a friend to ask his friends, but that won't do much. Hence it's obvious that boards have to be used for some things.
Whether it's warez, lifestyle, adult, medical or a tech board in overall, as long as it's easy to use, your members won't abandon you.
But this is the time you have ask yourself, are you sure that your board is easily usable? Does it have anything that members would be interested in? Is its design clean and professional?
Just think about it. Problem isn't with vBulletin at all, vBulletin, product, is material that will help you to build your board. It won't do much if you left it as it is, and it won't do much either if you add too many unneeded things.