I'm torn as to 5*. Nothing is guaranteed with it. Many times I'll at least get the Y-upgrade if nothing else, but I'd say that for at least 10 of my 25 rentals I got nothing more than what I rented. While that doesn't sound so bad, I can't honestly say that it's much better than the years where I was just a plain #1 Gold.
For example, at a station like LHR, it didn't get me much traction when they didn't have the car I reserved available (an automatic Avensis with Sat Nav), and I had to insist I couldn't drive a standard gearbox before they were willing to upgrade me into a nicer car with auto and Sat Nav rather than downgrade me.
I'd prefer to see a level at 20 rentals that had something guaranteed about it rather than amorphous benefits of the current 5*.
Steve