If you are thinking about expanding the information in Help, Command Documentation then I'm not sure the wiki is the best spot, as it would be duplicating the information thats already in the help.
Here's the help file from svn:https://bookscanwizard.svn.sourceforge.net/svnroot/bookscanwizard/src/net/sourceforge/bookscanwizard/bookscanwizard.properties
You could either edit that file and check in a new version using svn, or else send me the updates, and I'll check it in.
As far what is the most helpful thing that could be documented.. I guess start with the things that were a challenge to you to figure out. LIke I've said.. It all makes sense to me, so I do rely on others to tell me where things don't make much sense.
Though in any case, I'm happy with whatever you want to do.