The original poster asked what the inherently better aspect of Leica lenses was that merited their high prices. It's my understanding that Leica lenses are generally thought to outperform other lenses at wide apertures. That, if anything, is what you get with a Leica lens that you can't get elsewhere. Assuming that to be true, the question is: if you're handholding and using fast film in those situations (I'm guessing this is the case probably 95+% of the time, based on comments on RFF), how can you see this better quality?
Furthermore, it's generally true that all 35mm format lenses, Leica or otherwise, perform best at f5.6-f8 or thereabouts, and differences among lenses at those apertures are very small to nonexistent. Lens test after lens test demonstrates this. Photographers know this, and I'll bet the vast majority of pictures, when circumstances permit, are taken at those "sweet spot" apertures (narrow DOF being of minor importance except in limited situations).
So, then, how to justify buying a Leica lens, when its demonstrated superiority is only in certain rare photo situations? I think it has to come down to the perception of Leica quality rather than actual demonstrated better results, and the idea of owning "the best" rather than actual need for it. It's the same as owning a Porsche and never driving it at anywhere near its capabilities. "Need" = "want."