sadly the options for upgrading to later versions of vbulletin are well....like picking from two bad apples....and we simply cant continue to use this extremely outdated version forever, eventually it will simply no longer be supported.
What we will be moving to (xenforo) will still retain the same "bulletin board" feel, and the upgrade will not require anyone to reregister, nor will we lose any posts or data currently within vbulletin.
I believe someone mentioned in another thread that Disboards recently migrated from vbulletin to this new forum software as well, it is extremly popular and by most measures the most suggested and successful upgrade from vbulletin.
We hope it will expand the forum and make things more user friendly for both existing members, and all new members who find TUG!