Hello Dan,
I am a new buyer of 450H and went through some of the questions you raised above. In my case side camera, air suspension, ML music system, HUD, ACC/PAS, cooled/heated seats, heated steeting wheel as options nudged me towards the premier model.
I like the option of able to see the kerb to protect your precious alloy however you also get warning messages with side/front and rear sensors. I think your question has been well answered with regard to how the side camera works. It is an added bonus which adds yet another dimension to see outside your side.
I liked the way NX presents almost 360 degress view when reversing ... I think RX will get in coming years.