I don't know. I don't think players are thirsty for more diverse rewards, so much as they're thirsty for more diverse tasks.
If we had a system where we it was Get X from Y, and we had ten options for X and Y that were selected at random, then that's 100 quests. If you had a quest that's Get X from Y, and then Y asks you to first get A from B, and you have ten options for each of those, then that's 10,000 quests.