I was also a person who got it new back it the day, my aunt gave it to me. To be honest though I'm getting sick of all the earthbound crap going around. I think at the time of it's release it was underrated but part of that was due to nintendo, they didnt market Earthbound at all, and nowadays I dont feel as though it's "underrated" anymore.
To me the more you talk about how "underrated" something is, the more overrated it becomes. I'm not saying the game is bad by any means, it's great, but in all honesty the fact that cart only is over $100 for a pretty common game is ridiculous.
It's the demand that raises value and that proves my point that it's not underrated anymore.