This is one of those discussions that makes my head spin because the premise is so ridiculous.
How long has digital been around? Think about it. Go back 15 years and try and remember how many people were saying, "Why the hell are people using this technology? All the photos look like crap!!" None of them were, because it's an amazingly stupid premise (though I'd posit that it's a more reasonable comparison that yours, pairing two current generation sensors and assuming one is less capable).
Sensors in DSLRs from 15 years ago pale in comparison to what I have in my phone now. But my word, there are some amazing photos that were taken with them. It has so much less to do with the camera and so much more to do with the person using it. Know your gear and know its (and your) limitations and then exploit all the strong points. With today's gear, give a monkey a camera and decent light and even they can take a good picture. Don't believe me?
Every digital camera ever made is capable of taking a
good shot. Heck, every digital camera ever made is capable of taking a
great shot, or it wouldn't have come out. After shooting with my D7000 for a half year I spent a summer shooting exclusively with my iPhone because, heck, it was easier to carry on the road, and it takes damn good photos.
So, I would say that if you've moved up a notch and look back at a photo taken with your old gear and the best you can come up with is, "At 100% the detail is still pretty darn good if you ask me", then I would suggest that perhaps you should have spent more time and learned to get to "still pretty damn great", because that's what that camera is capable of, and a jump in model is not going to fix the things that prevented you from getting there with the D5300.
Now know that my intent is merely slamming you for your post because I realize, as you've said, that you're fairly new to all this and I have to assume your move to the D7100 had purpose beyond just getting better photos out of your gear. But I
need to be ultra-critical of the post because it's ridiculous stuff like this that confuses the crap out of people wondering about what camera to get, or what's right for them. More expensive, when talking bodies, doesn't always mean "better pictures". The differences in bodies deal primarily with available features and extremes in lighting and hardware, not with IQ. Grab the same piece of glass, a D3300, D5300 and D7100, and some good light and a nice subject and you
better be able to take at least a
good photo with each of them or you're spending too much time typing and not enough time shooting. Hell, even if you want to point to the DxOMark numbers and shout, "Look how much better X is than Y!!", you're failing to realize that the numbers are based more in how it shoots on the extreme edges of normal photography, and if you look at every current DX Nikon I'm guessing that they all score pretty damn high at ISO 100 with the 18-55mm at f8.
Know what it is you need in a camera before you buy, then learn how to use it by shooting it to death. If your pictures are only so-so, I'm willing to lay down some major pocket change that it's the operator and not the equipment, so make sure when you upgrade you're investing the time and money in the part that's under-performing otherwise, more than likely, you're wasting it.
Horse dead and well beaten.
