A lot of this depends on system complexity, I get the impression here that many have very simple systems. I've got two tape decks, a minidisc deck, tuner, CD transport, DAC, Streamer, turntable, phono stage, separate pre and power. That's 10 interconnects alone, 3 of which are play and record.
For fun I did try an old "freebie" interconnect between DAC and amp the other day (from back in the days of cheap 80's separates) and the difference was night and day compared to even an entry level Flashback cable for example. Genuinely shocked how "Grey" and undynamic a genuine Freebie cable sounded. Diminishing returns does kick in quickly though IMHO and it quickly becomes the case of something sounding different rather than better at the higher price ranges.