I have adaptive drive and I love it, on my 2011 35d. I extensively drove X5s without it, and the difference is obvious, especially on twisty roads.

If you truly want the best handling from your vehicle, this is probably the best way to do it, short of opting for 20" wheels and sticky tires.

I have 20" 214s and the car handles turns incredibly well. I've not pushed it yet, as the tires are still breaking in and haven't really been heat cycled yet (380-miles), but I have 100% control in places I've had to be mindful, even in 328i w/sport packages. I'm not comparing the two, but I'm simply stating the excellence by which adding adaptive drive (not to be confused with adaptive steering), adds to the enjoyment of the X5.

If you're a "driving enthusiast," the high cost is worth it, in my opinion. I think it should be a $1,000 option, and $3,500.00 is pretty ridiculous, but you have to pay to play with BMWs and their interesting options.