Is there any benefit to insulating the overhead garage door? We have vents in the garage, would that negate the benefit?
Sounds like overkill to me. I keep the window in the garage and the window in the door open a few inches for cross ventilation.
Actually I've found that putting a layer of insulation on the back/inside of the garage door made a big difference on the heat. At Home Depot you can get either the 1" foam board or they also have a foil wrap and either one would make a difference in my opinion.
Or you just might want to wait until you replace the door since there are so many newer styles and colors and window types than there ever were before and investigate the ones with the various R factors. We've noticed a difference with our new Wayne Dalton door and the built-in the door insulation is so much neater too. Sulley007's foam board sounds good too but I've seen sloppy fiberglass attempts that I don't insulates much and looks bad and collects/creates dust too.
Most garage door professionals will install insulation for a minimal charge, but there’s also the homemade approach, which involves cutting pieces of foam core and attaching them with double-sided tape. A layer of double lip weather stripping will help you seal the gap between the door and the floor. Besides the savings, insulating your garage door reduces noise and provides a more comfortable working environment