The only way I see this working is if you can replay stages at a harder difficulty.
I think the best implementation of risk/reward that has been in the Fire Emblem games is the simple addition of chests and enemy Thief's, among other map related side quests. As these chests usually provide some nice items but aren't exactly needed, and that they are part of the map and allow players to play the risk/skill or bypass it altogether. Beating FE without any deaths on higher difficulties is its own reward.
