Nevermind!
After posting I read the recent ticket about "move files after upload", and found Mars' suggestion to use the log for debug output, e.g. add "{.add to log| event upload completed by %user%.}" to the completed event handler. Works well and easily -- Thanks Mars!!
I used this to print out %item-name%, %item-resource%, and %item-url%. Looks like I can parse the URL to figure out which folder the upload is going to, and the -resource symbol has the windows file path rather than the VFS path.
Any other debugging tips are welcomed!
Steve