I sense the TS is just starting off and coming to grips with the various options to go in cameras...
Several arenas to venture to:
- different genre of photography
- capabilities of camera bodies - continuous shooting, time lapse, HDR, etc
- different lenses and perspective
If TS is not careful, this is going to be a big sink hole.
Some general wisdom
1. lenses hold value much longer, cameras depreciate madly once it gets out; so don't think about new camera unless it is limiting you in some ways (or your heart strings are tugged), e.g. you really need the higher mp for more resolution, or the camera controls are so much more superior and you need that, or you need low noise high ISO ability, etc. That said, DX lenses may be limiting if you go FX sometime in the future
2. it is the man or woman behind the camera that matters; upgrade your skills, read up, travel, go shooting with sifu and peers,
3. explore photography, not gear-acquisition.
That said, I recommend that you do 2. and 3. before thinking about getting new camera or lenses. Learning to cope with limitations of camera, learning to control camera, learning to see with the lenses you have, etc will yield long term dividends while getting new gears yield short term gratifications (unless you are limited by your gear already).
If you must go the way of gear for some reason, then
4. explore the lens set first, then camera later. You now have UWA, and I assume you have an 18-55 or 18-105, maybe an AFS 50mm f/1.8G (or AFS 35mmf /1.8G) might be a lens you could think about to explore large aperture work? Maybe a telephoto lens? Venture into world of macro? AFS 85mm f/1.8G and get beautiful portraits?
5. buy use where possible and confident. Especially cameras (but you must know how to spot lemons). If you want to explore fps then the higher spec bodies like D300s. That being the case, doing higher in the NIkon range will allow you to use AF and AFD with AF, and Ai and AiS and retain metering.
Don't always assume you will go FX and so buy FX now. FX gears are heavy and expensive. Buy used and good value DX will serve you well now.
In short, from where you are, the forward path is a several steps move, but upgrading skills should be the first step.