My thoughts:
1. I prefer manual/mechanical cameras.
2. I have used Leica but never an MP.
3. For a long time, I have wanted to own a Leica MP.
4. The MP is such a beautiful and expensive camera that I would want to collect it instead of use it. Therefore, I would be more inclined to get a user camera such as an M2 or M6.
5. My two “must have” Leica lenses are: 35mm f/1.4 and 90mm f/2.
6. I own a Nikon system.
7. I really appreciate the dependability and reliability of the Leica and Nikon cameras I have used.
8. I could never exchange my entire 35mm Nikon SLR system for a Leica rangefinder system; however, I would use a Leica rangefinder camera in addition to my Nikon system.
9. My manual/mechanical Nikon F2 with 35mm f/1.4 and 85mm f/1.8 lenses perform so well for me that they prevent me from economically justifying their replacement with a Leica MP equivalent.

My suggestions:
1. If your interest in the MP is as a collector, sell the Nikon system to generate the cash needed for the MP.
2. If your interest in the MP is as a user, get the MP but keep the Nikon system for a few months before you get rid of it. This will give you the time needed to determine if the MP will be able to replace your Nikon system.