I find it odd that posters correlate spending with audio quality, and that the question of a "sweet spot" is about the cost of an item. Of course, I get it that if one wants to "quantify" their audio hobby there are few ways to do it other than spend, but after many years in this hobby I don't believe that spend directly correlates to positive aural experience with a system.
I agree with the posters that say that synergy and engineering a system to taste, which generally takes knowledge, not spend, has a greater influence.
That said, note that I said "aural" experience above. I would tend to agree that spend does correlate to positive visual experience. In other words, expensive pieces tend to look pretty, or very cool, or very something else. Like those mono-blocks that look like droids. And with these pristine sci-fi looking setups, I am sure people love to just look at their systems.
My personal sweet spot is hunting used gear with the best synergies. My system is set up for easy swapping of component combinations. It ain't pretty, but it conveys a lot of knowledge and experience.