The astute Mr./Dr. noted the similarity between these two songs:
John Stewart – “Gold” (1979)
One factor that contributes to those two songs sounding related is the fact that John Stewart employed the services of two-fifths of Fleetwood Mac (the Stevie Nicks and Lindsay Buckingham fifths) to record “Gold”.
And when I listened to “Rhiannon” again, I remembered an Australian song that also messed around with the A minor chord:
Goanna – “Solid Rock” (1982)
Thanks, Mr. F, for supplying that coincidence.