Sorry for trolling, but I thought I add few notes...
I have owned several BMWs, none M3, and couple of P-cars to include a 987S and a 997.2 GT3 now. Also interesting to note a recent poll at Rennlist amongst GT owners show that nearly 80% came from M3s.
Although anyone can appreciate the comments about P-cars being expensive or not represent enough value for some people, I think couple things are being missed in this discussion: First, the price of any P-car depends heavily on options. If you try to price it by selecting too many options that really don't add value besides personalization, the prices climb easily above $120K. However, most owners keep their P-cars lightly optioned as the base car has more than sufficient luxuries, including the base leather. The only options you may want to spend money on and that also return value during resale are performance options. So, with that a 'nicely optioned' 991 911S is about $105K, I think that number has significant impact on "value" and that does not include usual discounts of $5-7K from dealer.
Second, the value equation is quite different for most owners than what is obvious on paper. A P-car has reliability and durability that few cars achieve. Particularly BMW is unfortunately not getting close enough in this regard IMHO. All of my BMWs had rattles after 20K miles, all leaked water from the driver's window after 30K miles, all had its interior trim fall off due to glue wearing out over time. I had no exceptions. A Porsche does not rattle even at 100K miles, it does not overheat, brakes don't fail and perform better than most performance cars. You don't have to modify a P-car to go to the track and be fast, safe and stay reliable, not even the brakes. And I am not talking about just GT cars, even Boxster and Cayman are built that way. When you put in six figures into a car, you expect these things, it is normal for P-car owners, but not for many other marques.
My BMWs never lasted enough on the track on any given session that I could really enjoy them. I could not even get enough camber to save the tires. From E36 to the last of E46 M3s had heat related issues, sub frame issues, brake issues still persist, electronic took over so much so that it is nearly impossible to work a BMW yourself anymore. For a P-car owner, at least a good portion of them, it is important to be able to work on your own car to at least change oil, brake fluid, spark plugs, etc. I do not know if you can do those things on a BMW any more.
I sold my Cayman S at 81K miles with 23K of them track miles. It had absolutely no issues when I sold it and I did not have to modify a bit of it expect adding additional brake cooling for my sanity. My 2010 GT3 now has 32K miles, it is my daily driver and has 10K track miles on it, no modifications. There are very few cars that can stand against it on the track. This weekend I had multiple 30-min track sessions at a heat index of 110 degrees, not a single issue, no P-car had any heat related issues at all that I know of, but most owners did, few were close to fainting in the car, it was so hot; I ran with the A/C on to cool a little more. Try that on a BMW... I doubt it would work.
I think most people that have not owned a P-car do not realize that much of the 'value' on the tangibles are not on a configuration sheet and won't be realized until you own one, any model. Although I have huge respect for BMW for what it stood for me in the years past, I have only one left in my garage and once that is gone, I don't think I'll have one again even though they still make attractive cars in one shape or another.
And also, how many other cars are available for which you can purchase a roll cage, carbon fiber race seats, fire extinguisher, etc. as options and still get to keep your warranty?