>>Everyone concur?<<

with all due respect, I do not.

while it may well be the case, it may well not be.

I did mean the standard head lamp switch, and asked about the DRLs because it can help narrow things down. the DRLs work when the switch is off, so had they come on when you switched them off we would have known more about the power path... but if the car doesn't have them, it doesn't matter.

maybe I've become confused, but did you say the the first sets of bulbs that didn't work were confirmed to have 'blown out'?

working with the air bag is not that hard. to be safe, disconnect the battery first, and then make sure everything is plugged in before you hook it back up, this way it should not log any trouble codes in the SRS (airbag system).

I would bypass the breaker with a standard fuse, 20 amp.
if it snaps, you can always hook the breaker up again, but at least you have a record that a short/high load did occur.

the next time you catch them not working, unplug both bulbs and check for power at either one (tan wire at bulb for low beam).
if power is there, plug one bulb back in and check again.
if the reading drops out, check voltage drop across the switch and the breaker.

I just printed out the diagram for the "SC" model and it looks nothing like the diagram posted above. what variant is that car?

>>Well, actually, they definitely are failing, at a much higher rate than they otherwise should, it's just that this *last* time they hadn't actually failed.<<
this is the part that confuses me.
if the bulbs are actually cooking, it's not an issue with any breaker, switch, or short. you just can't kill bulbs that way.