Great question, Giles. I remember seeing a couple other discussions on GovLoop that provide some insight from other members:
Do Rewards Damage Performance? https://www.govloop.com/forum/topics/do-rewards-damage-performance
Time Off vs. Cash Bonus? https://www.govloop.com/profiles/blogs/timeoff-vs-cash-bonus
My thoughts: I am mostly motivated by pride in my work and intangibles like being to able to telework/work from anywhere along with a flexible schedule. But I also really like to have a bonus structure in place that gives me some clear targets and an incentive for meeting them both at intervals throughout the year and at at year's end. The key for agencies is making sure the targets are really concrete and time-driven...because if it's nebulous and open to interpretation, that opens a big ol' can of worms!