Maybe the waiters only do 1 hr shifts, twice a week? So it's kinda like a hobby while they get to hang out with Janeway and co? - Or maybe it's x hrs of crap work per week if you want to in the crew at all (and at the bottom of the pecking order) ?
Emotion circuits aren't needed for motivation. It's pleasure and pain that drives all living things to behave as they do. That's why humans seek out each other, or why caterpillars eat leaves, or why birds build nests and why people do home renovation. -Beats me how you design a pleasure circuit though. Or a pain circuit for that matter.