Like @ghdprentice, my buying a house that had an unexpectedly good listening room was by far the most impactful addition to my system. And it took me about 8 years of living in our current house to figure that out. Right before COVID, I convinced my wife to take the big flat-screen TV out of our bedroom that is roughly hexagonal in shape with cutouts on two sides of the room (where our queen sized bed sits and opposite from that).and about 20 from wall to wall. There's only one 1st order reflection that I managed with a 2 inch acoustic panel. After that one tweak, my room is one of the best sounding rooms that I've heard anywhere.
Getting a Pontus II is up there in value as well.