While this is true to a certain extent, I think at this point it is more just a mindset. The M9 takes incredible pictures today, and will continue to take incredible pictures long after it's sensor technology is superseded. I think this is a camera that you could be satisfied with the quality of for many years to come, even though you may secretly lust for the latest greatest. If you really want a Leica, buying an older film camera is certainly an option. They are great cameras. And there is nothing stopping you from buying a film camera today and a digital camera later. The lenses will work fine with both. But you could also just wait until the M10 comes out later this year, and then find a great deal on a used M9 or M9P. That way you could get a digital M for maybe about the same price as one of the lenses.
Of course, having said all that, I can't wait to see what the M10 is going to bring. I am hoping for improved resolution and dynamic range, and maybe an electronic viewfinder with focus assist. But even if I purchase an M10, I am not sure I would get rid of my M9. May just keep it for a secondary body.
This is true. They are one of the most functional to use and well-built cameras available today. And the lenses are absolutely superb. The good news is that, while the lenses are very expensive, they hold their value and may actually increase in value over time. So while your investment in the camera may dwindle over time, owning the lenses is like having money in the bank.