I doubt very much that we will see any forum convertor tools soon for Tiki unless someone takes this up of course. I understand your concerns as I have a pretty large vbulletin forum and would not be able to switch to Tiki forums now. In the current state the forums are in, I think it's fair to say that they worth considering if you are starting out from scratch.
As to documentation: well you are looking at it. Tikiwiki is all about documentation and community work. Alternatively look at the sourceforge forums and/or mailing lists.