The carbon build up was mostly for early model year 2000 cars.
The clutches typically last 50K miles depending on who has been driving the car.
There are guys on m5board.com that have over 100K miles on their original clutches.
I look at it this way, i would rather have the clutch be the weak point in the drive line as opposed to beating up the transmission or rear differential.
The MAF's can be had for around $ 100.00 each if you search around. Those also last approx. 50K miles. Just remember, there are two MAF's on an M5 as compared to one on a 540i.
Other things; the stock rear sway bar brackets tend to break (better ones via aftermarket), front control arm bushings, and brakes are much more expensive than a 540i.