I decided to stick with that level of camera as the reduction in controls on the lower end cameras (my wife has a D5200) was forcing me to play more with the camera than getting the shot. I also have a great range of DX glass and didn't want to make the jump to FX.
As for using the D7100, there is a great improvement in the quality of the shots and the shots are much, much sharper to my eye.
However, that sharpness is a double edged sword. The D7100 is quite unforgiving for sloppy camera technique and I find I need to take care in shooting to get a satisfactory result. This typically means a higher shutter speed and possibly a higher ISO for what I'd use on the D80. Luckily the ISO performance of the D7100 is a world away from the D80!
I now refer to me D7100 as my scalpel, its razor sharp and will cut the user to shreds when used incorrectly