Heatsink compound does help. It increases the surface area thru which heat can be transfered between processor and heatsink by filling imperfections in the heatsink and processor. The amount by which your case temp would increase is negligible. Im not saying that an extra case fan wouldn't help, anything you do to lower temp is good, Im just saying that using a case fan INSTEAD of heatsink compound makes no sense.
Every dark cloud has a silver lining, but lightning kills hundreds of idiots every year who are looking for it.