At the higher end, parameters like resolution, clarity, soundfield nuances, bass impact, extension, etc can start to equalize, which are the same parameters that are immediately noticeable to a listener. Such equalization happens way more quickly with amplifiers, dacs, cables, etc. Subtle nuances don’t matter to most listeners, especially older ones with some hearing degradation.
At that point, you are better off improving the room and expanding your music collection. Or add a subwoofer, which can cause a drastic change...Or better yet, expand into object based multichannel audio/atmos, etc.
I believe it was Dali (could be wrong) that did a study where no one could distinguish speakers too much in a well treated room. If you insist on hearing differences that are wallet justifiable, get drastically different types of speaker designs. For example, i was comparing a TAD (concentric driver) and a Pioneer XY-3B (higher end PA horn that can bring down the house!) back to back in the same room for a bit. I could enjoy them for what they were... different presentations...could say the same with a recent Tekton
If i had been comparing the TAD with some higher end concentric driver like a KEF blade, it could have been a "why bother" moment, if i didn’t have a room that is capable of putting everything under the magnifying glass.....There are so many similar 3 ways or 4 ways which may lead you to a "why bother" moment....magico,...schweikert...Rockport...etc, Meh....