It isn't that big of a deal, I would suggest not to start throwing money at it at this point. It could be several things, wait and see what pops up down the road.
I disagree about the VANOS, the vanos clear symptom is if when the temp is below 50 you start the car in the morning and let it sit for a few minutes to warm up, the rev's will drop until the car almost dies and then surge back up. Sometimes it will die and if you don't warm your vehicle up the car will sometimes die when you pull up to a stop sign or light. This symptom will quickly go away when the vehicle starts warming up. Yyou would also not get a good strong acceleration when getting on it, it was unsteady if that makes any sense.
If you have not done any preventive maintenance on the t-case or transmission I would have the fluid changed in both. Drop the trany pan and have a new filter install and clean it out. You can buy a transmission service kit if you are a DIYer. The t-case is a bit involved as you have to suck out the fluid and buy the liquid gold stuff from a dealer IF you can find one that will sell it to you. Best to have dealer just do it. And, don't listen to any dribble about using anything except BMW fluid for either of these to items.
2006 X3 Silver Grey/Black Lthr/Alum Trim/Sport Prem Pkg/Xenons/Servotronic/Prem Sound/Satellite Radio/Heated Seats/Carbon Fiber Pillars/Blue Tooth/Aux In/Cargo Net/Aluminum Pedals/V1 Hardwired