35mm camera vs Digital DSLR with 50mm prime lens in manual mode?

I am very tempted to purchase a 35mm Leica IIIF but at the back of my mind I keep on thinking 'Why not simply use my Nikon D40x in manual mode with a prime 50mm lens?'

I simply cannot justify this purchase unless someone can suggest any advatage this 1950's camera would have over a manual set digital DSLR?