Hi Gary, good thread you've started. I've actually been in the same boat as you. I love the old Leica look, with the glow and just that touch of old school softness. Now for the bad news. My advice before you splurge a whole lot of money down on a D700 and a bunch of lenses is to go rent the camera and lenses first to try it out. Somewhere like
www.lensrental.com Why? IMO, it's not really a question of Nikon lenses vs Leica lenses and the look of it. In your case, I feel like it's going to be a situation of film vs digital.
In my past experience of trying to use old lenses on digital cameras, be it the M8 or the Canon 5D/1Dmkiii, the result was nothing at all like film. I can't give you the technical explanation as I'm not an engineer, but for me, the old school lenses on film looked right. On digital, it just looked like the whole images was out of focus. Is it because digital is so sharp and the tolerance for focus is so low? is it because digital has the tendency to be so high resolution that all the flaws in a lens like CA, fringing, that gave character to film images now come to light as what they truly are in digital? i'm not sure. I know one of the main difference for me between film and digital is the transition from in focus to out of focus is far more abrupt on digital to my eyes. This alone would make a pretty big difference to the ay old school lenses look.
Anyway, my thoughts are to rent it and try before you make the leap. you might be back to film pretty quick.