“Skip the grind” romhacks are the only way I play a lot of JRPGs. I don’t want to mindlessly battle to advance in the game. I have better things to do with my time, like playing a wider selection of games. I don’t need games’ length padded!
Not sure if it’s needed for Earthbound, but I’d probably just use it anyway. Most games set up a good leveling curve, so double XP shouldn’t break the game even if it’s unnecessary.