"Just take an average reading and preset your f/stop and DOF scale and go capture like a point and shoot"
Indeed! That's the reason why you don't need a build in meter in a M Leica.
The question was: "Trade M4 for M5"
My answer don' t do that because you don't need the build in meter of the Leica M5.
The meter don't justify the bigger size of the M5 camera.
And most M users find the M5 too big compared with the other M Leica's.
My main idea was that if don't need a meter inside.. as you compose, then, it can be used like any M with a external meter, BUT, if you find yourself in difficult lighting, the Built-in meter is very good and accurate, having a narrow fov, and is fast, because you keep your eye in the VF to adj exposure and framing. Plus with a 50mm, you have a center meter indicator to use as to what you want to meter. An MR4 meter is too wide for precise measurement, unless you are close.
If, you don't need a meter in the VF, any M will still do with an external meter. But, it gives you a option for a more narrowed Metered area than an External meter.
As far as trading to an M5.... Only if you like shooting in tricky light (night clubs, high contrast situations, where you need to expose for the subject only at a distance, or want more control on "What Is" really metered), Then, get the M5, if not, keep the M4/MR4.
I have an M5 because it the only M I bought years ago, but, I could not afford at my young age to add to it. But, I did enjoy the camera, and I very much liked the on board meter. But, I had no experience with other M models, so, the shape/weight/meter had no negatives for me. For, me, it was my 1st Leica, so when I could afford it latter on, I got one again. Sentimental, yes, but, I still like using it as my main film camera.