The heart wants what the heart wants! As long as you realize that your reasons are primarily emotional, and you don't expect the Summicron to be the magic bullet for your photography, then go for it. I'd be the last one to condemn anyone for putting emotion over reason, having done so on many occasions myself!
One's reasons may well be emotional, primarily or partially. Then again, they can be aesthetic, and artistic. The approach of "this lens outperforms that one at such and such an aperture" (often meaning one lens is sharper than the other) could be most important for some. It used to be, for me. But increasingly, we are learning to appreciate that lenses vary in certain characteristics, including some that we may have once regarded as flaws; yet they may deliver exactly what the photographer wants.
Some recent lenses for cinematography have become so clinically sharp that the directors and cinematographers don't want them. Leica, Panavision and others are offering them lenses with a pleasing balance that doesn't prioritize sharpness over other virtues. Director of Photography Alice Brooks needed a pair of lenses with a special quality not present in currently available motion picture lenses, a quality known as Flare. That's right, flare. She special ordered them from Panavision. Panavision asked her what color she wanted them to flare in. She told them, and Panavision delivered. To get exactly the image she wanted, she added Tiffen Glimmerglass filters to kill some of the biting sharpness of digital movies, and to add some more "glow". You can see the result near the beginning of the movie "Wicked" (go see it if you haven't), where the witch arrives in a bubble backlit by the sun.
I own and use three 50mm Summicrons. My 1950's version one collapsible, used wide open, gives me, at close distance, a lovely rounded soft-sharp look. It's not as sharp as my version four, but that's not the point. Then again, my 50mm Zeiss has a purity of color and a depth I don 't get from the Summicrons. And the focusing bump is wonderfully easy to use--and, as another member mentioned, the feel of the gear in the hand when shooting, counts!
So I think the way forward is to look for a quality we might call balance. Balance among the various characteristics we value. You know? OOh, this lens is too sharp! This one is too flat! This one is just right! And there is room for Ecowarrior's emotional attachment to a lens, as well.