What should i do with my camera?

First of all, i have a Nikon D3100 with 18-55mm VR lens, and an attaching wide macro lens.
The point is that i have an option of $1200 to buy a new camera or buying some essential lenses for the D3100. If i buy a much more imrpoved and better camera, by selling my D3100 with the already money i have, what could i get and should i do it?
Or if i shouldnt change my camera, what are the best lenses for a Nikon
I geuss a 50mm is great?

Added (1). Not a wide macro lens, just a filter* :D

I learned early on that high quality lenses make all the difference, Spend your money on lenses and once you out grow your current DSLR then upgrade that. A great camera will take less then quality pictures with cheep lenses. I can't help you with Nikon products. I shoot Cannon. As far as what type of lens, well it all depends on what you are shooting. Sounds like you have wide angle covered for now. You might want to look into a zoom lens up to 200mm. It would be a great addition.

Take pictures of stuff…

Yes, the 50mm f/1.8G AF-S is a better glass than the 18-55mm… The 50mm is a prime lens, you can't zoom with it.