I added an M9 to my D3 in 2009 and have both added a Leica M and a D800e since then.
It took me a long time to get used to the rangefinder focusing (I wear glasses), but boy has it changed the fun in photography (for me).
I would go for a Leica M. Only insignificantly more expensive but you get Live view and can therefore use your Nikon Lenses with a Novoflex adapter.
And the M is much easier to focus than the M9 - and I mean the rangefinder, not Live View. They did something to the rangefinder focusing mechanism and it's much easier and more precise (especially with the Noctilux wide open). As for the files, I like both M9 and M and in my humble view nothing beats these cameras for portraits (not kids) street or concert photography (security mistake it for a piece of junk, look at me with a pitiful gaze and let me in), creamy bokeh and laser sharp landscapes.
I still use the D800e occasionally for long exposures, Action (Children), wildlife and Macro, but I feel less emotion while doing so and it shows in my pictures. I may actually get rid of my D800e as I can now use all my Nikon lenses with the M (with Live View). I love my D3 though :-) it just feels right ... the D800 is just a bit too small for my hands
On the downside, the Leica M is heavier than the M9 and especially with the EVF, the difference to a D800 not that big anymore.
So in summary, yes go for it, but be prepared for a steep learning curve - especially with focusing. Something done much easier with the M than the M9.
As for the Fuji, I can't comment, never touched one.