It seems like gold is intended to be a max level grind to give you stuff to keep doing in the game, past the soul shards everything is just a choice of aesthetic or completionism. Besides you can farm 5k gold coins in like what seems like 30 mins with a full party doing high level enemy chains. I was in agreement with the gold costs at the start when im chaining 20 or so enemies at level 13, but level 27,28 enemies give like 14 each from the start, not including thief steal or ninja Dokumori the rate is probably at pace or faster than silver through CE's.