There are great reasons for upgrading , but only if you feel the need/desire! I never had a bad Nikon, and all of them with the right person behind them could make beautiful photos! But I upgraded anyway,with my desire looking for pro features, till now I have them in my D700, D800E and most of them in my D7100 good enough to qualify in my book! 
So upgrading is purely your choice, and is not a need unless you decide it is!
So upgrading is purely your choice, and is not a need unless you decide it is!