Are Expensive Balanced Interconnects Necessary?

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.

Most people can't help arguing balanced vs unbalanced even if the question is something else. 

My answer to the original question is that moving very far up the manufacturers line in either balanced or unbalanced provides limited or no returns but that both types of connectors benefit from good wire, good connnections, and good connectors so don't go with amazon cables.  

Cables do sound different, even in xlr configuration, it is up to you and the system if necessary.

Differentially Balanced kit means 2 totally independent channels (not touching each other), including 2 separate power supplies (one for each channel/L/R), but often a single PS is substituted. How critical 2 v 1 is I don't know, BUT,....

Doesn't it make sense that totally isolating the channels (no cross talk, or other potential compromises) would provide 2 pristine  channels? And if you understand that, THEN... how can ANY SE kit be true hi-end?