I honestly don't care about Ethers in this game, the only items that seem worth the money are Phoenix Downs, Elixirs and Cottages.
I might buy a couple Golden Needles as well if I have enough money for it.

I have only played the Famicom version though, so I have to prioritise things very strictly because the inventory space is VERY limited in that version, and every piece of item takes up its own individual space.