I have shot with every Nikon made in the last 10 years and any from the D90 and later is capable of shooting any image found on gallery walls. The D7000 was the first of the Sony sensors that were essentially ISO'less so shooting underexposed a few stops to get higher shutter speed when needed delivered the same image when boosted in post as shooting at at "correct" to the right of the histogram exposure. The D7100 going with a Hitachi sensor had better spec for low light but also returned to the bad old days of less robust file depth, meaning boosting in post usually ruined the image with banding and color fidelity loss, like a Canon was known for. The D7200 returned to Sony and it is a better data generator. But why are people trying to shoot at such high ISO numbers, even on the best cameras, DR and color depth goes to pot. Numbers being quoted are for 6 db signal to noise ratio, with if horrible.
I suspect the reason is few people print their images and on small screens even phone cameras seem good. But the question is, why record a dark scene and expect to present it as full daylight? That is not how our vision works and is creating an artificial presentation. Low light really does have noise visually, and poor color fidelity and poor edge detail, there really is less information with a camera or just your eyes.
Regardless of the camera there is very little difference between finished images between any cameras. Whether an image is worth looking at or tells a story, or draws viewers has nothing to do with factors the camera controls. If you create a compelling image, it is, without the camera having any impact on its interest.
Whatever you have, honing your skills at finding and telling a story, composing it and exposing as needed to best tell the story, you have a winner. Missing any of those elements and you have a worthless image even if pixel peeping reveals less noise than an other. Using that as a baseline, upgrading all the time seems to retard development of the photographer more than if sticking with a competent camera and learning to stories with light and shadow better. A good workshop or art appreciation classes at the local college will get you closer to creating compelling images far faster than buying another body.
Why are photos being taken in such dark where all the light information it missing anyway? Learning and using techniques to augment light is a more valuable skill than mastering a higher spec sheet camera. What scenes are needing that much artificial sensor amplification. Pro sports are very well lit, but that is the excuse most trot out as justification of getting a camera with 3million ISO. But look at their gallery and you see conventional snap shots or landscapes, cat/dog/baby pictures. It is gear hobby, not image hobby. Look around at images winning awards or in top glossy publications, ad work or any other high end or fine art images, what do they all have in common? MF, Fx, View camera, Dx, mega lens, or?? They all where that way because of light that was used creatively by augmentation. A studio is not a place where there are cameras....sure there are some but it does not matter which are used. Studios are where light is easily modified and augmented. Now, it is possible to carry a studio in your backpack. Look around your room, any images you see that were valuable enough to have been paid for, the difference in that photo that earn money and your snap shots is not camera but skill in telling a compelling story with light and dark. Light is cheap but requires learning how to solve problems with it and be creative with it. It is more open-ended than just buying a higher cost camera so it is less popular than just pulling out the credit card.
Is the D7000 worse than the D7100 or D7200? Technically, sure on specific single points that were focused on that by themselves have little or no bearing on whether a photo is good.
There are some simple steps to improving your images. One is stop thinking of images are pixels and components, they only make sense viewed overall, in one glance. If you can't see the whole image in one look without scanning side to side, you are too darn close. Every image, every painting, every sculpture has a viewing distance where it makes the sense the artist intended. It makes less sense if view further or closer. It is a human scale, and how we experience our environment. Go to a major art gallery with significant painting and you will see two types of people. notice some people move up very close, to see the detail and placard to see if it is famous. Many, particularly tourists who want to see a famous painting but know more about it when leaving than before seeing it because they get up very close. The painting has no information to impart to them, they get nothing from it other than they saw it. The other group of people see a large canvas and they move back, back to the range that it can be seen in one whole, as the painter intended. They are the ones getting something out of it.
The same with photographers, who are always pixel peeping to tell them whether it is perfectly sharp in some detail. They are ruining their own perception of their photo. Human scale of our environment depends very little on micro scale, our brains and eyes evolved to get the most information that was actually useful in describing their environment that would be useful to them. Actual sharp images often are less compelling than those less so, but regardless, how it looks as a whole is the only vantage point that suggests the message, story or feeling of the image. Stop pixel peeping and your stories will be better told.
Plan the intent of the shot or the goal. Shadow tells as much as light does, shadows is often ignored by those shooting auto modes wanting everything "properly" exposed. Hi ISO is death for shadows. If the subject is still, a good tripod is much more valuable than a high ISO camera.
A D7000 is a very competent camera and I dare anyone to look at a decent sized print and pick an image shot with a D7000 from one shot with a D810 when viewing from normal distance. Unless you are printing large and viewing too close to view in one take, the added resolution is just wasted, and adds no information to the viewer. A 6mpx file is plenty large enough for 20 foot billboards. If one photo is better, more interesting, it is due to content and non-camera reasons.
The most common excuse why people reject the suggestion to get into lighting is "I hate the flash look" or "I prefer natural light". Both only underscores the reason they need to learn about lighting. Every other image they see every day was done with lighting modification. That outdoor, sunny day beach photo on the magazine cover almost surely had lighting and modifiers used to create natural looking images. Snap shot without it, don't look "natural" at all, it is not how we see the same scene with our naked eyes. We use lighting and modifiers to trick the brain into seeing what would be natural for human vision but isn't what a camera natively puts out.
Another reason why upgrading all the time holds people back is because it consumes the budget that could be used for items that actually DO make a difference., such as workshops, lighting, modifiers, and even a lens of two. If you are not winning awards now, it is not because you don't have the latest camera. The reason the image that did get an award was honored depended not one bit on the camera model.