Well, that method:
http://dev.plexapp.com/docs/api/utilkit.html#String.Unquote
is only available when the python code is running as an agent or plugin. I missed that fact! My code snippet came from some of my own "external" scripts that interact with the pms ;)
In other words, use the built in Unquote function if you can!
Thank you very much. Updated both XBMC (TV & Movies) metadata agents to use that, instead of the dumb search-and-replace method I created while testing!