As people have been saying that the larger the sensor, the better the photo will look. Does the image quality really have a great disparity when shooting with a FF sensor and a M4/3 sensor which is about 4 times smaller?
Actually that is a misconception. What make up a good photo includes the following,
1) Composition
2) Skills
3) Story behind the photo
4) Image IQ (and that is only after the first three was accomplish).
For example, I can had one of the best system in the world and took pictures that are sharp, crisp and contrasty... however if the picture just looked like any you could download from the net or nothing special about it (or what I call... lifeless.) then it was all for naught. However, if another photographer who uses nothing but his mobilephone (say... a Nokia 1520 or 1020 - I like Nokia and I am not ashame to say so), to take a picture in the same area as me, but in the picture, he put in great thoughts, effort, the angle of the shots, the story behind the shot, the timing, the lighting, everything added in... and the picture had this "wow" effect that would glue audience to it. If you do a 100% crop, of course you will see my super duper sensor camera would produce much cleaner, sharper and contrasty picture... but overall it is just a multi-megapixel piece of crap, while the other photographer with a tiny sensored mobile phone, whose picture had the wow effect would certainly have more impact (visual) on the audience.
So... no... your photo will not look better even if you have a camera with the largest digital sensor in it. But if you are going just for the image quality... then yes, the larger the sensor, the better the image quality (to a certain sense).
However, it cannot also be said that big sensor camera are actually not useful or useless... if that was the case, no professional (photographers) would want to get the big sensor camera seeing that these camera system cost wayyyy more than mobile phone or compact camera. The big sensor camera like any other cameras is a tool and sometime you just need that tool to make your picture work.
I know M4/3 is a more matured system and plenty of lenses can be found. What I am thinking is that to use a FF sensor and probably attached a 4/3 lens over it and achieve the same result for a 4/3 while still retaining the benefits of a FF sensor?
Actually... you are pretty wrong in this area.
m4/3 had more lenses (native)... yes... that is correct. However, Sony don't just started out making camera. They have been making cameras and digital sensor for ages... need I remind you that Olympus fabulous m4/3 sensor are manufactured by Sony nowadays? Also at present moment the A7 and A7r didn't have much native lenses... with adapter though, you could add on other Sony DSLR lenses... which are very good indeed.
Plus... you must first factor in what you wanted to take... what genre you are after. After defining that genre, then you see if A7 and A7r current lenses supported that genre. If it did, I don't see what is the fuss... if it didn't, then you will have to make a choice to either get the adapter and purchase Sony DSLR range of lenses (but you will lost some of the advantage like being small)... or get the m4/3 then.