Having seen multiple approaches to this, I'm still looking for the common thread. I'm not sure if its a fault, by design etc. Without decent screen shots before/after etc I can't make a clear decision either.
The Rift doesn't appear capable of actual full-range - some dark greys/black are clipped by design, as the panel manufacture is not perfect (smaller pixels = more variation when compared to the much larger pixels used in monitors/OLED TV's etc).
Some are using high-bandwidth adapters to force the full colour range.
Others are plugging in their regular monitors into the HDMI port their Rift is using, setting the display properties and then switching back to the Rift. i.e. they're finding the Rift HDMI port reponds to port-specific settings, since the Rift doesn't respond to a windows-monitor settign as it doesn't show up to the OS the way a regular monitor does.
I think a lot of the threads describe very subjective quality differences - some may think it looks better while in reality theres a quality loss - but others describe a definite improvement.
I'm hoping to try my work HDMI monitor cable at home (currently I use a DVI cable on my home monitor) to see if the NVidia control panel settings do indeed make any difference.