Really depends on what you consider to be an "upgrade".

When I made the jump from DT770 to LCD-2C I was a bit disappointed. My expectations were that of a linear upgrade in the same way you would get with upgrading a graphics card - I was expecting to literally hear more sounds in my music, which was not really the case. It was more like I was able to focus better on the subtle sounds that I already knew were there, but there wasn't too much brand new information I could substract from the track.

From that point of view and at that time it didn't really feel worth it. But at the same time that's a somewhat limiting way of looking at it.

Now take that same LCD-2C, EQ it a bit to add a few more db in the mid to sub bass region as well as a bit of treble, and then pair with a record such as Infrared Horizon by Artificial Brain. That EQ combined with the 2Cs relatively intimate yet at the same time thunderous soundstage, its bass extension characterized more by a sense of audible vibration rather than slam, alongside that subtle "plucked" sound specific to plannars, and you get yourself an experience that is so different from the DT770 that may as well arguably worth x4 times the price depending on your preferences. It's not downright better in the same way that upgrading from 60 to 120 hz is better or from LED to OLED is better, but it's such a different way of experiencing your music that it can be worth it, very much so or somewhat so depending on your personal preferences.