Thank you for explaining your process. I know you said you were following the guide exactly, but that doesn't mean you weren't overlooking or misunderstanding something. I don't think those internet/date 'fixes' are valid...those don't even make sense. Have you rebooted the computer at any point in all of this? Especially with removing old drivers and installing new ones, even if the computer doesn't ask you to, a reboot might be needed.
It sounds like when you reconnect the phone, it's not recognizing on the computer for some reason. When you do the unplug/replug, try unplugging the cable from the computer, not the phone, if that's not what you were doing already.
To answer your question about success rate, nearly every single person on here has done this at some point. This particular thread is only a couple days old. Here are the previous threads on the subject, in chronological order, if you would like to trudge through them. The process is exactly the same for the flash tool part.
http://androidforums.com/threads/official-restore-with-dl-mode.853693/
http://androidforums.com/threads/how-to-restore-phone-with-dl-mode.861292/
http://androidforums.com/threads/the-so-you-upgraded-to-z4-and-lost-root-guide.874943/
Whatever you do, do not attempt to run the flash tool is update mode as stated in the 'official restore' post. You will end up with a factory reset status 2 error and you'll have to start completely over. ONLY use board mode.
I understand you are frustrated, it is frustrating trying to help you without being able to see what is going on on your end. Please be patient and understand that we are doing something that isn't exactly intended to be done and is somewhat blocked by the manufacturers. It's not always going to work perfectly.