If you decide to use spoke prep, there's a neat trick that will apply just the right amount of prep on the spokes every time. If you use too much it makes the nipples bind and is probably worse than leaving the threads dry.
Take a cheap, large diameter ATB inner tube and cut a 2-3" section out of it. Take the cap off the spoke prep bottle and slide the whole bottle into the tube section so that the rubber stretches over the open mouth like a drum. Now poke a pinhole in the middle. To apply the prep, just poke the threaded end of the spoke through the pinhole and draw it back out. This will wipe off the excess prep, and leave just the right amount in the valleys of the threads. You probably want to clean the inside of the tube to avoid contaminating the prep.