Its a pure nostalgia play aimed at tapping into the brains of people who first got into the Pokmon trading card game as kids when it started, have probably since fallen off, and now have nieces, nephews, or kids of their own, and enough disposable income to be willing to spend money to relive their childhood glory days, or at least get back that beloved foil card they lost, traded away, or had stolen back in the 90s
5E Fifth Edition 0 - Common - English ME4 #101 M10 #121 BR #0 4E 3E 2U 2E 1E Commander, Legacy, Modern, Pauper, Vintage Alchemy, Brawl, Competitive Brawl, Historic, Pioneer, Standard, Timeless
More recent sets also have lots of ways to make treasure tokens, which deal with your mana fixing problem early and give you lots of throwaway artifacts to sac to Breya in the mid to late game
It's hard to say, as we haven't had anything like that in the game yet
Japanese Unlimited copies generally cost less than their English counterparts, especially in PSA 10