There are quite a few writers cheat sheets out in the ether telling one which key to write in to evoke a specific mood. There's A LOT of overlap, edge fudging & minor nuance involved in the same.
I have a couple of them saved somewhere as they were sent to me by well meaning people but I don't use them. My chord choices determine the mood, & therefore lyric, of a song for me. That is unless I was aiming for juxtaposition as I was in my most recent finished song & video.
A keyboard allows one to conjure more "colour" or mood as there are, usually, ten digits to use in voicing a chord.
As to the piece at the centre of the discussion:
"This gives the piece an added sense of mystery and beauty, as the subtle shifts and nuances in the melody create a unique atmosphere." This would be subject to interpretation and exposure. I doubt I would hear any nuanced mood in the piece as, after hearing it flogged to death for so many years, I shut off. It would probably take a different key or interpretation for me to pay attention.

Cheers
rayc
"What's so funny about peace, love & understanding?" - N.Lowe