Before I gave up engineering for Apple a decade ago, I asked myself a question: I spend much of my time using computers for the sake of computers: testing them, finding their limitations etc... When do I use them to create? I fell into a common pattern, which is to contemplate the tool rather than use the tool to create. I'm a gadget guy, and often am enamored with equipment. However, when I left that world I vowed not to use a tool for the sake of itself, but to focus on what it can do for me artistically. I don't "covet" my cameras as possessions, nor keep those things that don't provide artistic utility for me. This may be extreme, but it has helped me to focus on the output rather than the tool.
That said, I often find myself asking "When should I take my 5D and when should I take my MP?" The answer boils down to "what's the job at hand?". If I *need* to get the picture - to trust that I'm not going to miss the shot... If I need a quick process that results in the best images in the shortest amount of time, I carry the 5D. Sure, it's big with that 85mm 1.2 lens - but that's the right tool for me. If I want to experience the analog photo process for art reasons, or work quietly, or am going to a place without plugs for recharging, I grab the MP. No one camera can solve both issues for me (yet). The M8 is great, but it's just not yielding the results that my 5D does (please note: this is not a dig on the M8 at all! for me, maybe it's totally the tool for others!!)...
So, I feel your angst. Fight the urge to get caught up in using a camera for the sake of itself and grab whatever gets the job done for you. For a while, carry them both... You'll know based on what gives you the best images in the end.
I've noted that the Leica's are an amazing object unto themselves. They feel good - they're built so well - I enjoy using them due to this. But (again, this is just for me!) if compared purely in terms of the images they give, I grab the 5D for it's sheer reliability, full frame and low light brilliance and to "get the job done without worry".
Don't grab a camera based on how much you've spent on it or how it feels in your hand, or even how much space it takes up in your bag (within reason, of course). Grab it because you utterly enjoy the images it produces.
This is a totally subjective opinion - there's nothing wrong with using a tool for the sake of itself - and for many, Leica IS the best tool for the job.
These days, I just want to create great images and tell my story - I don't really care what tool gets it done as long as one of them does :-)
The M8 is the first camera and lens combo that made me consider a break from my current tool. But I can't get the same images out of it that I can with the 5D/85 combo - and I can't replace it overnight if it breaks.
I hope this helps a little in your search - good luck in your creation!