I figured it was time to put the D7000 back into action for shooting wildlife since I keep wishing for a tighter field of view (fov) than, say, the D600 + 300mm + TC-14EII = 420mm. With this combo attached to the D7000 it is 630mm equivalent fov.
So while it looks as if the negatives outweigh the positive ( 3 to 1), I'll use this combo again and again until I acquire something better because it obviously satisfies to the point that this one positive is of greater value to me than the three negatives are deterrents.
The big downside I'm finding with both my full frame and cropped sensor cameras at this point is weight. A sad truth is the body and lens combos I have are heavy for a day in the field and more so the older I get. In fact, they're heavy for just being out a few hours with anymore. To top it off, the D7000 (DX) body is a little heavier than the D600 (FX) body and I mostly use FX lenses on both because Nikon has really let DX down on this point so there is no weight savings to be had here.
I am fully aware of the new cameras and lenses (smaller, lighter) on the market now and keep tabs on what is happening. I hope one day to be able to make a switch to one of these competent smaller, lighter systems. That's right, systems. A camera body is no good without proper lenses to go with it. And some out there are sorely lacking in lens selection right now (Sony and Nikon DX come immediately to mind).
It's all relative and what works for you may be different than what works for me. I enjoy being outside shooting wildlife, close-ups of plants and flowers, some landscape and portraits so it's a pretty broad range of lens focal lengths to cover these areas. If you've got any insights or comments I'd like to hear them.