These days, rangefinder photography has little to do with logic. Go with the camera your heart tells you is the right one. In the long run, you'll be happy.
The MP and M6 have the greatest "fun factor" for the act of taking photographs that I've ever experienced. I believe the M7 may detract a bit from that fun factor.
Aperture priority isn't going to save you a lot of time. Rarely, will it make a difference between getting good pics and not. Its amazing how fast you can get with a fully mechanical camera when you become familiar with it and use it often.
Based on my past experience with a G2, I don't trust electronics. Although there are plenty of M7 users who have never had a problem, you read far more posts on these types of forum about problems with the M7 compared to the M6 or MP.
If you get an MP, it should last a lifetime. There is something special about a material thing being with you through various stages of your life. Musicians feels much the same way about their instruments. You can pass the MP onto your children. I don't think the same is true about the M7 -- eventually its eletronics will fail for which their will be no spare parts.
Before the M7 was introduced, one of the consistent arguments in favor of the Leica Ms were their mechanical nature, albeit with a meter. This dealt with durability issues and forcing the photographer to make conscious choices. Many of us still feel this way.
If you want aperture priority, the new Zeiss Ikon is probably the best bang for the buck, especially if you wear glasses.
I echoe the prase of Tony Rose. He has the best best prices and good service. Grey Market MPs are in the $2500 US range.
Both the M6 and MP are fun to use. I've used them both extensively and currently have two MPs, although I've never paid Leica's horribly inflated MSRP. You will pay about $1200 US for a grey market MP over a mint M6.
If what Leica says is true, then the MP is more durable then the M6, which says a lot, because the M6 is built like a rock. When developing the MP, Leica supposedly (according to Leica) took the M6 apart and asked themselves whether each component could be improved, and made the improvements. Leica also guranteed repair parts for the MP for 30 years.
Although I have two MPs, I probably would have been just as happy as keeping my M6s. I would rather have an older body and current optics, because Leica's current lenses are phenomenal.
It sounds like the reason you got out of digital is to get away from electronics. Why would you go back to relying on electronics?
If I were you, I would get an MP or M6 and see how it goes. If after 6 months to a year, you find yourself missing too many pics, then you'll know what to do.
Have fun with whichever direction you go.
