That sounds perfect! Keeping the gold a player incentive instead of a required score (excluding of course losing if you bankrupt) sounds like the best choice, as on further consideration the openness it allows the player is one of the reasons I've liked this demo so greatly!
Having the gold rewarded be scaled to potion complexity could lead to players restarting until they can get the most complex potions for each traveler anyways, so it's probably better to leave that out haha.