This problem started gradually, where at first I could count on the car
turning over a few more times than usual gradually getting worse until
finally it will not start at all when it's wet...moreso when it's cold and
wet. It turns over fine, but will not fire.
OK, I've replaced the distributor cap and rotor. I've also sprayed the ignition system with a "moisture-displacing" silicone spray. This seemed to work for a short time. The lead to the coil is black and guncky on the inside (where it connects to the coil, not where it connects to the distributor). Could this be the culprit? Someone also suggested that one of the coil connections could be comprimised. When I take a blow-dryer to the ignition system, the car starts, so I think it's definitely a moisture problem...but I'm unsure as to what exactly...
Think about it. You've already isolated the problem knowing that when it's
wet it won't start but if you dry the ignition components with the blow it
starts right up. You already have the answer but just don't know it.
Strange as it may seem, we can't see your car from in front of our
computers but you can.
With the car running in a darkened area (outside at night, in the garage with the lights off, etc) take a spray bottle of water (like a plant sprayer) and lightly spray in the areas of concern ( coil, distributor, plugs wires). When you see a fairly spectacular light show or the engine starts to miss you've found your culprit.
Not knowing the mileage of your car (my '85 Jetta is closing in on 400k miles), or how vigorously it has been maintained, it might just be time for an ignition system overhaul. I hope you replaced the cap and rotor with good quality parts. Some of the junk you get from Autozone, etc is worse new in the box than a 250k mile Bosch part.