This one is a little tough, as we don't know yet if Leica has been able to make their new CMOS sensor "sing" with all those legacy lenses, but for argument's sake let's assume that the new M240's IQ is at least equal to the M9 (although I am hopeful it will be superior). There are obviously advantages in higher ISO, live-view, focus peaking, video (if desired), weather proofing, faster processor, larger buffer, better LCD...but I believe the major advantage is the EVF. I realize that you have indicated that an EVF is not a factor in your buying decision, but I believe it will be a major benefit of the M. The ability to have focus peaking, zoom to focus, diopter correction (without the need for $100 screw in magnifiers, and use wide and telephoto lenses without optical finders is a major benefit. Also there are many people with less than perfect eyesight (like me), and using a rangefinder becomes more and more difficult with age. For those reasons I like the new M.
The big unknown as of today is how the CMOS files are going to look compared to the CCD. I expect Leica to answer that question very soon. If the IQ is superior it's a pretty easy decision for me. If the CMOS files however don't have that "Leica look" that I'm used to then I will just keep my M9 and live with no EVF, lower ISO, slower buffer, etc.
A few more months should answer the question, however there is no guarantee that the M240 will be available anytime soon. Mid-2013 is not unrealistic. If you don't want to wait that long then a new M9, M9-P (while supplies last) or M-E is your best option (because of the warranty).
Stephen
PS I expect M8 and M9 prices to continue to fall next year, as owners trade in and sell their cameras to purchase the new M. The M8 is especially susceptible to further price drops after Leica announced they will no longer be able to repair defective LCD screens.