This hack will add an experience counter to each characters’ Data window.

I found it annoying that the original game never told you how much you've accumulated, aside from telling you how much from each fight.
Facing limited ROM space to insert, the display isn't polished. It'll show leading zeros, unlike the rest of the numbers, and it'll be blank if you have 0.

Still, I found it more useful than nothing.
I've included two patches: one for the original Japanese game, and one to apply on top of j2e's translation which can be locates on the link below.

http://www.romhacking.net/translations/217/

Sted - Iseki Wakusei no Yabou (J).nes - GOODNES 3.14
CRC32: A86FB17A
MD5: D838580E334C5977DFFDDBA07827AA06
SHA-1: 3B2364F2CF804D2B114C4382C14A99BCB990227F
SHA-256: 55C2C02541C85B7B154A2E8662DE4AF2D7FDA0CF470471616B5E23524125B038