To me the Beyer DT880/Senn 650/AKG701 the old classic toprater, does nor really bring much improvement over the cheaper bunch..
If we move another step up the likes of JVC DX1000/Audeeze/HiFimen/Stax/HD800/T1 etc etc you get an improvement that is worth while, if it is worth the extra money is another question and not something I can decide for others than myself, so I have decided to get some of the heavyweigthes and have fun with the cheapline, much cheaper than buying all the expensive ones..
So IMO if you are going to save for a GOOD phone do so, but do not go for the midpriced ones, go for one of the >500$ phones otherwise stick with the cheapos, the difference between a good Chinaphone and a 300$ phone of the more normal brand is not big enough to justify the extra 200$..
It is only my oipnion of course, others may have other views on the subject..