Okay, I have a little rant here.
Please feel free to skip ahead to the next post.
With respect, I do feel you're overstating your case. (And I'm not sure what Mustangs have to do with the topic.) I don't see how buying a $60k+ (new) car should mean that the prospect of having a non-serviceable critical component like a DCT, which if it breaks could mean a ~$15k repair bill for wholesale replacement, shouldn't make you blink.
If money is no object, then maybe you're not planning on keeping your M3 for long and don't sweat the drive-off-the-lot depreciation of always buying the new car that's under warranty, or perhaps you're buying cars with another zero added to the price tag. As sweet as the M3 is, it's in the middle-class price range, and it's even one of the more affordable cars among BMWs. People here spend money on their cars, perhaps more than most, but I don't think that means people here don't value that investment.
And a car like the E9x M3 is, for many, an automotive investment. Yes, anything BMW may strike some as being too ostentatious and indulgent to be a reasonable car purchase. The thing about BMWs that they, and even short-term BMW owners, may not appreciate is that the engineering is pretty amazing and that BMWs tend to last. Over the decades, well-cared-for BMWs have proven to be a good investment in terms of having a quality, stylish, performant ride for years and years and miles and miles, for less than the cost of flipping for a new car every three years. (It's also an investment in the joy of driving such a great machine.) The BMWs that don't last are usually ones with particular pernicious engineering problems with a particular crucial component.
I agree that the S65 is a complicated engine and may prove to be expensive to maintain. But so far the engine is proving to be a winner, one of the best to come from BMW. The 6MT is a variation on something BMW has been doing for decades. On the other hand, while yes, so far the DCT is looking to be solid, it's still new technology without a lot of high-mileage data points, and with "lifetime" fluids and not much in serviceable parts, it's a black box.
I prefer having the track record there.
I also happen to like manual shifting, especially on a performance car.
So yes, I consider it quite reasonable for people to weigh the various factors that can play into the long-term value of a car, even the current M3.
My current M3 is not my first M3, nor is it my first BMW. My 1998 M3 racecar has 150k+ hard-driven miles. I have a 13yo 5 series still running like a new car. I had an E21 with close to 20 years and 200k miles on it, running fine and looking great, before it was totalled. And I had a '11 M3 with DCT, and had no complaints, aside from some of the nanny features, and it was head-and-shoulders better than the automatic on the 335xi I leased a few years ago and also loved. All of them are great cars, and I wouldn't consider any of them only for their short-term value. And I wouldn't deign to say that anyone who values money invested in a well-made car is somehow in the wrong class and shouldn't buy an M3. It's a BMW, after all!
This the unbiased
opinion of a BMW fangirl, offered with a smile. Rant over.