Are Expensive Balanced Interconnects Necessary?

Balanced interconnects work best with differentially balanced components.  Check to see if your stuff is. 

If you stick with Mogami or Canare wires, you are assured of neutral cables. If you like the rest of your system, that's what I'd recommend. You can have cables made to your exact needed lengths and save a ton of money over the "boutique" brands.

If you are looking for flavoring, by all means try the boutique cables and be prepared to pay accordingly.  The ones I've tried all did funny things to the sound. Not my cup of tea at all. So I think the "Clearly" in your first sentence would better be, "I think" or "Some people think" or "Cable manufacturers say."

my short answer is sometimes, but generally not nearly as important (as unbalanced rca ic’s)

btw, nothing in high end audio is necessary, the entire hobby is not necessary -- to have the means and desire play with any and all of this is a luxury in life

yes

I've been using balanced cables in pro audio applications for decades, and when recording the audio for a TV show some years ago I swapped out some pedestrian cables for a set of new "expensive" balanced cables. Immediately heard an improvement (good headphones tied into the mixing board...live feed...you can hear the musician's heart beating). Mo bettah sounds mo bettah, and dats dat.