What date in 2011 is the backup from?

I am not sure if upgrading will fix your issue, as I truely don't know what was done to your site to cause this issue.
If your site is not very busy & you think you will not lose many threads/post installing the database backup then I would suggest installing it.

I would suggest submitting a ticket on vbulletin.com & explain to support staff exactly what was done to your site to cause this issue & see if they can offer a better solution.
Also, link them to this thread for a quicker understanding of your issue.

In the future, create a copy of your database daily or weekly just in case issues like this come up.

When you removed the plugin, did you also remove all files from the site that were added for the modification? If you aren't sure, then please go redownload the modification and go through the installation instructions backwards.