Part of the Leica/Leitz history is that they single-handidly popularized the 35mm format. Before that, if you wanted decent photos, chances are you were dragging around a large format rig with bellows, ground glass, etc all on a tripod.
But until Fuji came with its X series, Leica was the only game in town for rangefinders. The use of a rangefinder arguably helps for some styles of photography, especially street shooting and portraits. This alone could be worth a lot depending on what one gets from photography. The was a good review by Steve Huff detailing all of that [1]
Also, until Sony pushed its more compact line up, full frame cameras were bulky ugly heavy tanks riddles with buttons everywhere (like the Nikon D3 [0] for instance). Leica cameras were the odd simple and straight to the point tools blessed by top notch sensor technology.
[0]http://kenrockwell.com/nikon/d3.htm [1]http://www.stevehuffphoto.com/2010/08/04/my-updated-big-bad-...
That's true, but the variability is much greater than is commonly appreciated: http://www.lensrentals.com/blog/2014/07/sensor-stack-thickne... :
While I don’t have a mathematical formula to predict how well a given lens will work on a given camera, it should be apparent that wide-angle rangefinder lenses designed for film are going to struggle, especially on m4/3 cameras, but to some degree on other cameras. Longer focal length rangefinder lenses tend to have longer exit pupil distances and should do better. Stopping down to f/4 or f/8 should reduce the problem significantly, although it isn’t guaranteed to eliminate it near the edges of the frame.
SLR lenses may also have some troubles on m4/3 cameras, since there’s nearly a 2mm difference in stack thickness. They shouldn’t have as much of a problem as rangefinder lenses, though, since they are designed for a 2mm sensor stack and they tend to have longer exit pupil distances. Older lenses designed for film cameras will tend to have more issues, of course, since they were designed for no sensor stack.
So much misinformation as usual anytime anything comes up about photography.
yes rangefinders are prefered (or were) by street photographers because the cameras and lighter and smaller, the lenses too, with the mirror box to overcome the lenses can focus much closer to the rear lens element which makes for lighter, smaller lenses. The main reason for their success in street and journalistic photography was because what is moving into and out of the frame is visible at all times, and in crisp clear focus, no matter where the lens is focused. if you shooting a tank rolling into the city center its better to know what else is going on around you and you don't want to have to focus the camera before realizing you're going to get run down by an M1A1 Abrams.
Please let's confuse retrostyled with rangefinder. That doesn't the Fuji X series aren't good, they are, for an APS-C sensor they are decent performers with some nice lenses.
The great advantage of a rangefinder is this: With some practice and experience you can _reliably focus_ the camera _without putting it to your eye or pointing it at the subject_. You can do this because the lens rotation stops at both far and close focus points and you can judge the focus distance by feeling the relative position of the finger tab on the lens, or by looking at the distance markings on the lens.
The other advantage of the Leica is the simplicity of the manual controls necessary for photography: Aperture, shutter speed, focus, shutter release. Unfortunately Leicas are becoming increasingly complex with the addition of video and so on to the M model. Not that I mind new designs, but I think they should also make a more affordable model focussed on simplicity above all, something like [this](http://hypertexthero.com/logbook/2013/09/design-good-camera/).
When I am asked what camera is best to learn photography with I always want to and do recommend a Leica, but I do it with a heart weighed down by the knowledge of the price of the thing.