The best thing you can do to improve your images is to learn more about photography. No disrespect intended - I try to take this advice myself. Practice practice practice. Take some good courses if you can. Not "how to use your camera" but rather things that are artistically oriented. Go to lots of exhibitions. Buy some books of the great photographers and study and absorb them. Learn to critique you own pictures and find someone who can give you reasonable feedback. The internet forums including those on this site are useful up to a certain point.
I am frequently amazed that the more I practice the better my equipment seems to get.
This is not to say however that better equipment doesn't help. And the lenses are generally more important than the body. One of the reasons you think the images coming out of the Leica M8 are so fantastic is because they have Leica lenses in front of the camera too. A single Leica prime (not zoom) lens probably costs more than all your equipment combined. An M8 plus 3 lenses costs quite a lot more than my car. Those lenses are the best you can buy they are made and tested by craftsmen and you never ever get a "bad copy".
So after looking at lenses you might well consider a new camera body too. If you fancy spending a bit of cash there is no shortage of options. The Canon 5D is amazing value for money if image quality (rather than a long list of features) is your top priority; it has been a fantastic camera, and the fact that it is now 2.5 years old and being sold for about half of what it originally was listed for makes it an amazing deal. But it is very unforgiving of low-quality lenses.
The best thing that happened to my photography was getting a 5D and the Canon 50mm f1.4 prime lens. Very good value. Extraordinary IQ, not too heavy. IQ broadly speaking on par with the M8 (better in some ways and perhaps slightly worse in others). At probably about 1/4 of the price. Stick with the 5D and a 50mm fixed focal length lens for 6 months and if your photography doesn't improve beyond all recognition I'll eat my hat.