Is "image quality" the ultimate goal in photography? What exactly is image quality? Is this a good picture? (from
Vivian Maier Photographer | Official website of Vivian Maier | Vivian Maier Portfolios, Prints, Exhibitions, Book and documentary film) but there are blown highlights and motion blur! Yet it is still great work.
A camera is a personal thing. What focal length do you shoot at? How does it fit in your hand? Do you need speed of operation? Do you fight with the camera, or does it just work for you? etc. I'm not sure the measure of cost vs. "IQ" is useful, to be honest with you. Even if we defined IQ as (resolution + DR - noise), which is how most techno-photo-netizens seem to be measuring it.
Having said all that, I think there are two improvements in the c3/5n vs. the 3/5: 1) better micro-lenses (needed for such a short flange back distance) means sharper corners and less color shifting, 2) higher MP means better resolution, and Sony has done this with little to no noticeable increase in noise.
But for me, all the other items I mentioned (fit, comfort, etc.) leans me away from the NEX. I did try the NEX C3, and found it too small for my hands, so I'm sticking with M43.
On a purely dollar play for resolution and dynamic range, I think the C3 is a very good deal, if the size works for you. If you stop worrying too much about ultimate IQ, then the older 3 model is a bargain. If you want something more expandable (i.e. you can add a viewfinder, etc.) then the 5n is really nice. I never liked the 5 that much, and in terms of cost vs. resolution&DR, the sensor in the 5 was not any better than the 3. It was more about the grip and size.