Upload & Sell: Off
There are too many lens that are similar to Planar with minor performance differences, Nokton, M-Hex, to name a few. But the look of Sonnar for portrait is different, gentle to the skin, modern coating, a kind of 3D look with round object without being harsh. So it is on my "do not sell" list while I can comfortably swap a Nokton with Planar or M-Hex without missing any lens in particular. But if you don't shoot portrait, there is little reason to keep it.
Agreed. Everyone must remember that this lens is an updated version of a lens from the 30s, and, while it may be a little sharper than the vintage version, as the design is slightly different, it's the updated coatings that really separates them. I use a ZM 35/2 on NEX for my sharp, corner to corner, Planar-like, standard lens on NEX, and the C-Sonnar is more of a people lens, unless one wants a more "classic" rendering to their landscapes and such, or if one is shooting a scene that has various objects at different planes, because the lens is sharp when actually focused into the corners. The C-Sonnar has a unique OOF character compared to my other lenses, which is great for a 75mm equivalent lens, IMO. If I was shooting an M9 or film camera, I'd likely be using the 50 Planar...or maybe both.
If you want a sharper wide open 50/1.4 rangefinder lens, you've either gotta go Summilux ASPH, or Nokton 50/1.5, although, interestingly, on the 5N, the ZM 50/1.5 is actually sharper than the Nokton 50/1.5 in the corners past wide open, if you actually focus into the corners. The ZM just has so much field curvature that it isn't good for flat field subjects until f5.6, and then it still isn't great. For whatever reason, I've never warmed to my Notkon 50/1.5, and I've been meaning to sell it forever.