I owned an M8 for a couple of years. I had been using an Epson RD-1 and from the moment I purchased the M8, the Epson sat on the shelf. The M8 produced great images. I purchased the M9 only, and I mean only, because of the crop factor. That was just an important issue to me, and I have been very happy with the M9. However, none of the issues that the M8 had as Leica digital RF 1.0 (IR filters, high ISO noise etc.) kept me from enjoying the camera, and if it had been full frame, I would probably not have upgraded based on IQ alone.
If I were making the decision today, and the crop factor were not an issue, I would just get a Fuji X-Pro 1. Seriously. The chip in that camera is superior to the chips in all cameras from five years ago in a quantum sense. Better high ISO performance, higher resolution, movies, etc. The camera has higher motor drive speed, panoramic mode, autofocus or manual focus at your option etc., etc. The M8 was an amazing camera for its time, but times have changed.
Now. Having said all that, if you want an M8, there will never be a better time to get one. Sometimes you just have to scratch that itch. One of the tragedies of the digital age is that when a camera comes along with which you just "click" there is a tiny little window to enjoy it. Seriously. You want to enjoy a 75 year-old M3 DS? No problem. You want to enjoy a digital camera after 75 months? Don't hold your breath on finding a battery that works, let alone spare parts. Ugh.