Here is my opinion:
In good conditions, with proper exposure and technique, it is almost impossible to tell the difference in image quality between dx and fx.
In poor conditions you might be able to see a difference in a side by side comparison.
That said, I also think using the right tool for the job will most often produce the best result but, in this day and age who would even notice.
I see horrible sunset photos go semi-viral on facebook, out of focus, bad horizons, over saturated and poorly composed and the average viewer loves it!
I think my point is, we photographers, especially pixel peepers are perhaps overly concerned about things that our audience wouldn't even notice.
Even knowing this won't stop me from seeing all the flaws in my images and buying new and better equipment because I want to be happy and proud of my work. I am however trying to put more effort into the subject, composition and emotion rather than worrying about a few pixels in the shadows and....I think I will stay with dx to do it!