NAV-TV has a solution if you are looking to add a Backup Camera to your Porsche Cayenne -

The PCM3.1 is a fully automatic backup camera interface for 2011 and Up Porsche Cayenne. It also works on the 2009 and Up Porsche Panamera.

A second camera, such as a FLIR night-vision, front or interior (child) camera, can also be added to the vehicle with the purchase of an additional video switcher, and manually selected on the PCM screen.

However, this second camera will not operate while the vehicle is in motion; to have a second camera that operates in motion requires the PCM3-AV970 kit.

Read More at the Manual



new 2011 Porsche Cayenne RVC + iPod video demo - NAV-TV OEM Integration - YouTube

 

Is the camera any better than the stock one (resolution, color, etc)?

 

The NAV-TV L-Cam and Handle Cam for the Porsche Cayenne offers an alternative and comparable solution in regards to the stock camera -

 

I was looking on here a while back to see where I should go and buy a good factory integrated backup camera for my cayenne year 2011 and the only one suggested was Nav tv but that was way out of my budget. So I did a little research and found another company called Jemko systems selling the same OEM factory integrated cams as Nav Tv but more around my budget. Can't complain it works really well. They sell 2010-2012 models I think.
Good luck!