I am spritzing mine because I am in a very dry climate and having a really hard time keeping the humidity over 40%.
It's a test batch, so if I don't get ducks I wont freak out.
WZ, I'm in CO and have been keeping my incubator humidity high throughout incubation even for chicken eggs. Buster is in ID with similar climate and he thought it improved his hatch rates... I have a mixed batch of duck & chicken eggs going now and the humidity is staying around 60%. I think the eggs just dry out too much internally if it's not kept high.
I am interested to know how your hatch goes, as it sounds like your humidity is running quite a bit lower than mine.
I don't know anything about hatching ducks...but I am reading Storey's Guide to Raising Ducks and it states that spraying them helps them to dehydrate properly. I think I would spray them but maybe watch the aircell's to make sure they aren't getting to big. If they start dehydrating to much stop. I would also maybe add a wet sponge to help raise the humity up to the right level. Humidity seems to be very important in hatching ducks.
I am debated on getting ducks. I am thinking about Khaki's or buff's or maybe Appleyard's. I can't wait to see how your hatch comes out.