What you're talking about is called a dopper rig. They're commonly used for perch, and sometimes crappie. Perch feed on minnows whenever they're available, so the the flash of the spoon attracts them to the area. Bluegill, on the other hand, almost never feed on minnows. They key primarily on insect larva during the winter. A dropper will work on bluegill, if they're agressive that day, but isn't as effective as it is for perch. If the gills are neutral to negative, the spoon will scare more of them away than it will attract. Anyway, that's from my personal experimentation.
kerosene