Isn't this whole approach to coffee similar to audiophily? I'm asking this as an avid coffee drinker (fancy grains, with a fancy machine) and an appreciator of headphones as well : when should one stop the quest for perfection? For headphones, anything beyond 400-500$ is not reasonable, since past this limit you start chasing gains that are barely perceptible or are a question of taste and you'll be able to find equivalent headphones that cost less.
Where do you draw the limit personally ?
I have a 200 EUR handgrinder and an Aeropress. That's about the limit for me, there isn't really anything else to improve there for filter coffee. There's probably a lot more ways to make different coffee, but not that much room for making the same coffee better. I also don't want to mess with the water, so that puts a ceiling on coffee quality anyway.
There's some legitimate room to spend much more money when making Espresso. But a lot of the more expensive options would be more about the workflow than quality. If you need to make many Espressos in quick succession you'll hit the limits of cheaper equipment.
I think it's very comparable: the current dialogue in "coffee" circles revolve around the usage of "steamed water" that supposedly improves the taste. I remember similar discussions around cables in audio circles.
My cousin bought a used professional coffee machine that looked like a piece of industrial equipment - tread plate and all.
Most of the time he would ask you if you want your coffee too sour or too bitter, but this one time he managed to get all the parameters so right, that he brewed something which tasted like thick, coffee soup.
Outright teleported me to 1960s São Paulo to which I've, BTW, never been.
I've been chasing this taste ever since, but my cousin still hasn't been able to repeat the feat.