I suppose I could make some spreadsheets and calculate an optimal way to complete the game for a higher rank, but I really don't see the point.

It would go a LOOONG way if there was some sort of permanent prestige bonus for every time you completed the game. Little things like a 0.5 bonus multiplier to chaos or a 25% gather speed bonus. You could offer more powerful bonuses based on rank

Hard mode could offer even more substantial bonues for hard mode.

As is, I'm probably not going to give it another go.