My plugs were still perfect at 42K miles and unless you know you have a coil issue by a CEL you have carbon on the valves. The PCV leaks oil fumes when you back off when running the hell out of it. That is what overwhelms the current PCV and many use an oil catch can which if you go with a better quality PCV available for around 50 bucks will most likely solve the problem.
This the upgraded PCV I will be putting in after taking it down for intake valve cleaning.
You might want to consider getting this once you get the valves cleaned.
If I was you I would tell the dealership the truth that you like to run the car hard because after all it is a BMW and that you think the valves have build up from being a direct injection engine. Also a lot of Audi's and VW's are suffering worse build up than BMW with turbos.
Hope this helps...