I've never been a fan of rangefinders, and I'm not convinced that a Leica is worth the price. Sure, you've got lenses that can whip the piss out of a good deal of other lenses, but that only means anything of you have the technical dicipline (and I'm sure you do) to get the most out of them. Still, you're dealing with a 35mm negative; unless you know that you really need the compactness and silence of a rangefinder, you might be better off buying more (or better if you dont have Nikon's highest-quality) lenses and more film. You could even get a pretty good MF setup for the price of a Leica, and the bigger negative is another plus
But that's just my opinion. And to put my opinion in to perspective, I shoot Pentax K-1000's and have no reason to get anything "better".
I learned on SLR's, so I like how they work. After learning on an SLR, I cant get my mind in to rangefinder mode. Other people have less trouble switching than I do. I think that's worth noting.