Your question implies that you have had bad experiences with your D7000 and see something in the D7100 that you were not getting. Is that the case or am I misreading what you are saying?
As far as older cameras, as an example, I have used far less capable AF systems without issues, such as the D70s and D200. Still, new capabilities open new possibilities.
I have shot the D600 under candlelight level lighting, at ISO 6400, and gotten consistent in-focus results, (and this is with the AF Assist light turned OFF). That's with the 24-85mm VR, btw. I have also used it on fast moving wildlife, such as Canadian geese with my 70-300MM VR at f/8 to f/11. It locks on and stays locked on. It's a very capable AF system.
I'm mildly ambivalent on the bracketing capability requirement. I used to be one of the original moderators for the HDR forum here and once upon a time, created thousands of HDR images with both 3 shot and 9 shot bracket capable cameras back when the DR was much lower than it is today. I couldn't find a difference in final output in a carefully prepared capture and post processing workflow. Folks like Thom Hogan think 9 shots is actually too many, (I believe he prefers 2 shots). I would not argue that conclusion from my personal perspective.
I don't shoot HDR but rarely anymore as it is hard to find any application that accurately reproduces colors - besides, I find the D600 has so much DR, I can get the shot I want without the extra hassle - I have gone back to using a GND if I think the DR is going to be too much.
Just a perspective,
"Extraordinary claims require extraordinary proof " - Carl Sagan