The big change from 09 to 10 was newer iDrive system and screens. I'd go for 10+ model years, as that change brought significantly faster processor and response of that NAVI/Camera screen. It used to take many seconds (up 10) on my 2008 X5 for the camera to come up when I put car in reverse, now it is ~2 seconds on my 2011 (which has similar software & hardware as 2010 model)... So, if your wife really values camera (as she should for such size car), go only for 2010+ model.

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His : 2013 X5 3.5d Deep Sea Blue/Black/Aluminum with ALL packages, 20" 214"s, running boards, Adaptive Drive, Spare Tire, BMW Apps
On Order : 2016 X3 3.5 MSport Silver/Mocha with DHP, CW, Prem, Tech, DA, Lighting

Hers : 2015 328xi MSport Silver/Red

Prior:
2008 X5 4.8
2011 X5 3.5d
2010 335 xDrive
2013 335 xDrive