I wouldn't say it's a false sense of accomplishment seeing as how Nightmare mode in this game is still easy relative to other games in the series thanks to the party system. There are no tangible benefits, no, but the combat feels more rewarding on at least Hard because easy is hard to fail on with three characters and items. Other Ys games are unforgiving. Felghana is hard on Normal mode.
Go to Gamestop, buy a Steam card, and use it to purchase Ys Origin. You won't be disappointed. For more info: http://www.worldofys.com/yso/
I wouldn't say it's a false sense of accomplishment, it's nice to play through the same game with added difficulty. I don't do it with all games, but it's super fun to challenge yourself with Ys games.