My X3 was a CPO so the extended warranty was added into the asking price but I really debated on whether or not to go this route as my last car was a CPO and I never used the warranty in the 120k miles I had it.
CPO was not the deciding factor in buying the X3 as was the very low miles it had and I was able to deal down the price low enough that it probably covered most of the CPO. My only tough decision was whether or not to purchase the extended maintenance plan as it can be very expensive if you go through the dealership after the initial maintenance plans runs out. I didn't purchase it as it can be purchased later.
I think the decision on buying either the extended warranty or maintenance plans depends on how long you intend to keep the vehicle.
2011 X3 xDrive35i F25 (CPO) Space Grey/Black Leather, Packages: Premium, Cold Weather, BMW Apps, Sirius and Technology. BMW CCA Member (WindyCity Chapter). Former cars: 06 750i E65 (CPO) 07 E90 335i (bought used but had problematic iDrive so sold it to get 7-series)