Is the C/Y 50 1.4 (MM)Planar the same optical formula as the new ones offered is Nikon F mount and EOS mount?
Datasheets for both lenses are on the Zeiss site.
The MFT curves are different and the cutaway pictues are similar but very slightly different.
Yashica/Contax (Rollei?)
http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/Planar1.4_50mm_yashica_e/$File/Planar1.4_50mm_yashica_e.pdf
ZF
http://www.zeiss.com/C12571FF00438F7A/0/4DBF8F5EBA9BB366C12576930030E0A3/$file/planar_14_50_en.pdf
You might like the image quality of the Nikkor just as much or more, but it's definitely not the same. I'd say the difference is of the same magnitude as between a Nikkor 50/1.8 and 50/1.4 (any of the many types). Neglible to some people but important to other people.


And seriously, if you "can't create art" unless you use Leitz lenses, you ought to see a doctor. 
