You pose an excellent question, for which there is no right answer, everyone is different. I think as you go up the expense ladder, particularly with electronics, the qualitative differences are real, but narrow significantly. You may spend a good amount of money to get only a 5% gain but for some people that will be money well spent, others not so much. For some, the chase is the game and is unending.
This is also relative, not absolute. Someone who owns $50,000 speakers might think they are in such rarified air that all that can be achieved has been achieved. The fellow who owns $100,000 speakers would think a little differently.
in the final analysis, it’s not a competition, something we sometimes seem to forget. All of us have a different budget and a different amount of money that we are able and willing to spend on this hobby. The goal should be to deploy those resources in a way that brings you the most enjoyment. Some will reach a place where they are perfectly satisfied and get off the train. For others, the journey doesn’t end and they always look for the next upgrade. Neither is wrong