I was experimenting with restricting multi-user linux boxes.
A few days later trying to run QCAD with the above security settings threw this error:
QInotifyFileSystemWatcherEngine::addPaths: inotify_add_watch failed: Permission denied
I had to go back to 755 on /home to allow QCAD to show the file chooser dialog (e.g. when you select File ==> export bitmap)
Looks as though the QT app requires world readable to work.
So stopping people listing the /home directory may only be a workable solution on a shell access only box.