I think that's a difficult thing to generalize in such a way. The last time I upgraded, I upgraded my cartridge to a much higher level. Later I upgraded my phono-stage, but that was because I added a second tonearm and needed two inputs. The phono-stage upgrade was great for the cartridge upgrade but not necessary for that reason alone.
It'a about striking a good balance in the end. There is no good rule of thumb.

