Some comments:
1) it is very often expensive to get the last little bit of quality. No matter if you talk about cars, audio equipment, cameras/ lenses - I believe there are some great lenses from other brands as well, but I am pretty sure that nearly all the Leica glass is exceptional. Of course its not twice as good, but it is very good
( by the way I believe the same is true for the x1 - which is slow but still IMO the smallest/lightest camera which delievers such good IQ and a special user interface (matter of taste))
2) price is one thing - value the other. Leica lenses are very stable in value
3) IMO the important thing about the S2 is that you can use it for a wider range of taking images. Because of the different form factor, weather proof design and it is also quite responsive, plus the lenses are relativly fast for MF and you get a little more DOF so you might have to stop down 1/2 less than with the large sensors - so you gain about 1 f-stop.
Is it expensive-yes. Now this will sound strange but I say: Many people who can spend 20k for a MF-Kit could also find a way to spend 25k for a S2 kit - it would be more important that the system does what the user wants/needs. And here the S2 offers some advantages and some disadvantages compared to MF.