Id consider myself a rather large M fanboy and ill tell you the cars are money pits. Yes the Vanos loves to go out with no prior warning, and last I checked there was no permanent upgrade to fix the problem. The S62 loves to eat oil, and its picky, it needs that Castrol TWS shit which is like 11dollars a quart, ive seen M5s with 50k miles eating quarts every thousand miles, not a huge cost, but it adds up. oh and the valves like to get carbon buildup, and they have weak rod bearings like the S54s do.
Suspension wise because the car is so heavy it eats through ball joints. My buddy has done his every 35-40k miles on his, and its not cheap since you cant replace just the balljoint and its something like 300 bucks per control arm.
Last did we did brakes on his car it ended up costing around 400 bucks in parts just to do the front.
Its just not worth the extra headache over the 540i/6.