Zeiss seems to feel that Aspherical elements are not necessary in most cases. They do bring a whole new set of problems, a tendency to flare, expensive to make and nominal, if any improvements in resolution in "normal" focal lengths.
Aspherical elements have become a bit of a catchphrase with Leica and it is also a marketing gimmick. I have the 50f1,4 Asph and it is a stupendous lens as is the 75f2 Summicron Apo Asph. I have had 21/2.8 Asph, too big and rather clumsy and the ZM 21/2.8 is just as good, without flare problems. The same thing goes for the 24f2.8 Asph. - very good lens but it was always left behind because its size and performance wise the ZM 25/2,8 is its equal. The 35/1,4 Aspherical (first version) was very good, but way too much money and the 2nd version had severe flare problems (i tried two of them and both could "opaque" out an image if you were unlucky).
The 35/2 Asph is extremely sharp and contrasty and I like the size, though it is heavy compared to the version IV.
The 90f2 Apo Asph was a good lens, but it was inconsistent in its performance. Aperture and distance would affect the performance and it could be very good or mediocre, depending.
I have very little experience with the 28f2.8 Asph, but the few shots I have taken with it looks good.
My favourite "pack" at the moment is the ZM C-Biogon 21mm f4.5 (most likely the best 21 ever!), the 35/2 Biogon ZM and/or the 35/1,4 VC and the 50f1.5 C-Sonnar.
I have played with the 85mm f2.0 ZM, but I found it big and rather clumsy to use and my feeling is that the 75f2 Summicron is a better lens.
However, a C-Sonnar 85f2.8 would be a nice complement to the pack.
Keep in mind that I shoot only black/white and if you are shooting color the results will probably be different!