Folks have covered the better nature of the D7100 - it's a generation or two of sensors ahead, as is the D5300. The difference between the two has more to do with features, and I believe were you to shoow with either of these you would see a difference in image quality.
Should you upgrade? I don't know - do you want to upgrade or do you need to upgrade? My recommendation is you should never get a new camera simply because you think it might improve your photographs. If you are completely satisfied with the photographs you are taking then you have exactly the right camera already. But, if you find there is something you want or need to do that your camera is not doing as well as you'd like then upgrading is a completely valid move. From the sound of things, there is nothing on the horizon that seems to scream, "Wait for me!!" - the only rumors point to a pro style DX which will likely be about 2X the cost of a refurb D7100 or more. So, even though the D7100 is 2 years old, it's still something that Nikon is unlikely to replace in short order (maybe this time next year?).
If you're looking for some inspiration I'd recommend looking at a new lens, like an ultra wide (8-16mm, 10-20mm or 11-16mm). But if your equipment meets your current needs then keep shooting until that changes.
Thanks Jake. A few valid points here. Do I want or need. Good question. I'll be honest and check the want box.
Improve my photographs? I don't know. I came from point and shoot to DSLR. I have no experience (other than my old K1000) to judge myself by.
New lens is certainly an option that I am keeping open.
Does my equipment meet my current needs? Absolutely. Do I want (not need) bigger, better faster? Hell yeah