My own .02....
I shoot a D700 and an M6. I can't justify a business model that justifies spending triple what the D700 cost for the same or similar results (nice, smooth digital files). If the M9 magically shot better pictures than I could make with a D700, I'd be all in. If I spent $7000 on an M9, only to return home and see files I could have made with a camera at a third the price, I'd be utterly disappointed.
The M6 and b&w film produces a result that is unique to digital cameras. That's why I like it so much.
Also, at $7k for a camera body that wasn't weather-sealed and didn't spend it's life in a studio...well again, just another crippling feature. Would you use an M9 if it was sprinkling out? How about at the beach or lake, where water mist blows?
I'm not a huge fan of developing film, and I have very little patience for scanning film...however, Leica M's built their reputations on simple, reliable cameras which could go anywhere. The M9, at the end of the day, is an extremely expensive digital camera whose technology will be outdated in the next upgrade cycle, and won't have the reliability M users always depended on.
Ask yourself (rhetorically)...are you happy you spent $5 grand on an original M8? It was the greatest thing since sliced bread upon it's introduction.
If you have money to burn (and that's not a judgment...good for you) then by all means get an exciting M9. You'll have man-jewelry to make any camera label-watcher green with envy. If you don't have money to burn, back your D700 up with a Fuji X100. It's small, lightweight, affordable, and specs out like a D300S with a Nikkor 35/2 strapped to the front.
---Dave.