Utilizing OEM upper mounts is usually to keep a nicer ride quality, especially when the car sees a lot of street time. Aftermarket pillow ball upper mounts are usually used for track setup suspension as they create a harsher ride. It's obviously not as easy to install when you have to swap upper mounts and modify them, but that's the trade off. Also, KW has the Clubsport model (maybe not for the 3IS), which is one step higher than the V3 and includes pillow ball upper mounts.

 

Good stuff, well done