I have played earthbound many times before I played mother. If you are a huge fan of the series, yes it’s worth playing. But it’s not necessary, earthbound is almost more of an enhanced remake than a sequel. Sure, there are some differences, but nothing compared to mother 3.
Actually happened to me too. I’m pretty far into the game but I made the mistake of trying to play 2 JRPGs back to back. The older I get, the less I’m able to grind that much. I have to switch up genres between my main gaming love of RPG to something else in between to not get burnt out.