I own both a D7000 and a D800. The density of pixels are the same and at 100% crop of the same scene with the same len,it produces similar pictures ( the D800 is a little nicer but thats probably due to the EXCEED 3 processor)
Just beecause the D5200 has a higher pixel density (equivalent to 57.6 meg in an FX camera) doesnt mean you get less noise etc.
I did find the D7000 a visible stepup in dynamic range ,Noise and color from the D90 but I wonder if the sensors can improve much more due to the size of light waves etc. Clearly advances in signal processing will occur.