Hi,
I'm a sucker for new kit but I'll play devil's advocate on this one. I doubt very much if you'll see any difference in picture quality from the D5300 compared to the D3200 -
here is the DxOMark sensor comparison. Unless you already have Nikon's best quality lenses you might see much more bang for your buck by upgrading your glass.
I'll add the caveat that I've used neither camera.
Bob.