(warning, I haven't read the rest of the thread yet)
As a webdev, my current favourite tool for new sites is Drupal.
SMF would be a very good option to upgrade these forums since it evolved from a project to port YaBB to PHP: transferring the content of the current forums shouldn't be as hard as switching to a completely different forum system. I imagine there is probably already a script to convert yabb2.2->SMF2...