Robert, I would prefer classic to perfect design
but you raise a good point.
I think some of it would be the long model run and the ease of updating/backdating, good availability of parts, small number of well built cars, hold their value well, and pretty decent performance even is stock form.
The longer you own one the more you appreciate it. Then comes the slippery slope to personalizing it. Then it starts getting expensive when you try to improve it.
After a couple of years you realize there's very little reason to replace it. Besides, no one will pay you what the car is worth to you, much less for all your improvements.
To some it's a hobby, to other's it's therapy, and for a few of us chosen one's there is no difference.
My wife tries to explain to her friends that at least it keeps him off the streets and out of the bars.