Without going into dollar amounts, there is a limit on what I will spend on "anything". Just because I could afford something doesn’t mean that I will buy it. The cost limit applies more to some of my countless hobbies and less to others, but applies to all of them, nonetheless. They all reach a point of diminishing return and satisfaction for the dollar and that point varies per individual. They key is to have the wisdom to know where that point is and enjoy what you have.
How good is good enough?
Most of us here cannot afford six figure prices for each component (assuming that will bring the best sound.) So how far do we want to go to improve our systems? There are always bigger fish. When does it stop? It stops when we say it stops, when our gear brings us satisfaction. To constantly strive for better sound is an endless quest, not necessarily based on the quality of our set but on our personality.