- Like what you've got: probably stick with it. It's only a probably here because we've gotten much better cameras recently and your choice of these models indicates you're a bit of a serious photographer to start with. You'll probably appreciate some of the things the new cameras give you.
- Dislike what you've got: You have two basic choices: (1) stay with the same type of model and get the current version (D7200); or (2) move up to FX.
Which should you do? Here's the simple guide:
- Choose #1 (buy a D7200) if you're happy with what you've got in terms of camera ability but want to upgrade simply to update your equipment and get better image quality and performance. Be prepared for some surprises if you're moving from 6mp to 24mp, though. Things have changed a lot since you bought your camera. You may need to replace some lenses (the 18-200mm is one such candidate). If you’re a bargain hunter, a D7100 is a very good choice while it’s still available new, as it gives up very little from a D7200 while netting you a steep discount.
- Choose #2 (move up to FX, most likely the D610, maybe the D750) if you're now serious enough that only the best possible image quality will do for your next camera. Be prepared to have to upgrade your lens set, too, though, especially at the wide angle end.