This is subjective based on room size, room acoustics, and the audiophiles ability to discern subtle differences in sound quality between brands and components,
for as you go to higher price point equipment, the absolute value of the performance/price ratio becomes smaller. Differences perceived important to one listener may not be important to another. That said, from my personal perspective a spend of around $75k should get to 95% of the best of the best. If you buy preowned you can take 30% off of that spend. To me, I believe my system is at the 95% performance level at a retail cost of around $90k and a preowned cost of about $45k. I would have to double that spend to achieve a 2 or 3% improvement and much more because my small home and listening room would need expansion to accommodate the equipment required to achieve improvement. My home is my limiting factor. My weakest link now is my server/streamer where I would need to double or triple my spend.