I'll assume that it's possible to absolutely destroy this game, no matter the platform? I recall becoming waaaay friggin' strong. I think what I did was work several weeks in a row for that guy in the first town, & then put the $ in the bank, worked a whole lot more, until I got stron enough to battle the guards in the castles, so that I could loot the treasure's, & then put that $ in the bank, & worked alot more, & then just did upgrade after upgrade after upgrade. Nothing could touch me, though, I may have still been vulnerable to instant death hits. You do ofcoarse get wayyyy old doing this, meaning you're stats go down a bit as you age, but, since you have so much money's, you can still become stronger then anything in the game.
IIRC, there was a $ exploit in the SNES version. A friend of mine had it, & I think there was a way to keep recieving $ from treasure chests or something like that...