Have you tried putting RainEx on your windshield? It is a silicone compound that apparently fills in the microscopic pores in the glass causing the rain to bead up and run off. It also helps the wipers be more effective. Just wash the windshield clean and then apply following the directions on the bottle. You may have to reapply every month or so in wet weather.
And ...
This may sound silly but are you sure the fogginess isn't on the INSIDE? You could have a small coolant leak in the heater core causing coolant to condense on the inside of the windshield. Also the A/C is supposed to come on when above a certain temperature and you select defrost. That is supposed to dehumidify the interior of the car. Maybe it's not coming on.
HTH
Brian
