An M6 is a fine camera that can take Leica and Zeiss M mount lenses, so it is true that you can make wonderful captures, but it is not an MP and does not feel like an MP in operation. The only thing I dislike about my MP is that it does not have the larger shutter speed dial of the M7, which makes it slightly harder to operate.
I've had a K1000, and numerous Canon SLRs and DSLRs and for me, none of them match the quality of images that I get from Leica + Leica or Zeiss lenses. The SLRs also don't have the pleasant shutter sound, especially at lower speeds. When compared to digital, nothing matches the simplicity either. Holding the camera will further persuade you to own one, it's small but solid, the feeling of quality.
You will undoubtedly get a variety of opinions, most I suspect trying to convince you you are unwise both fiscally and emotionally. But from an actual MP owner, I can advise you that they are correct. And that it does not matter, as you will appreciate the MP. If you do have the funds, consider the a la carte program so you can customize the MP and make it yours.