I can offer advice in the other direction..
My 528i rolled 183,000 the other day.. Starting about 30,000 miles ago I noticed a big drop in fuel economy as well as a stumbling idle when it was cold. No engine codes at all. I replaced CCV, ICV, Plugs, etc.. Still didn't fix the problem (although I solved other unrelated things).
Then I rebuilt the double Vanos with a kit from
Beisan Systems
MPG went from 23ish up to 27.5+
Idle problem solved
More Power below 3,000 rpm
Generally smoother
Moral of the story, if you have less than 120,000 miles I probably wouldn't do it yet. Any more and I would. The gas mileage savings alone will pay off quick. Now if I could only get 4 more mpg out of my X5 somehow..
