What are you looking for in your upgrade? Do you like the menu driven interface you have now? If so, d5200 may be a better fit. If you want to get deeper into photography, the d7100 has more direct access to camera controls via buttons. It has a front command wheel and buttons for quick changing of settings like iso, focus modes, metering modes, exposure compensation, white balance, bracketing, picture quality and flash modes without getting into menus. It also has an internal focus motor so you can use many older lenses. If this interests you, go for the d7100, you will love it. But it will take some practice to get used to this new setup.
If these things DO NOT interest you, then a d5200 will give you more focus points and a better sensor, better low light performance, etc, but with an interface the very much same as what you have. D5100 to d7100 is a great upgrade if that's what you want. Mainly it is an upgrade of your shooting experience. Don't do it just for the hope of better pictures.