As Zed sed :-)
It seems most of the absolute, no-parking available days are the result of coincidence, like massive conventions, holiday weekends and very warm weather all happening simultaneously. Or the obvious crowded times of the year when plain common sense tells you that the park will be crowded, and attendee beware.
The APs add cars, sure. But clearly they also add funds or Disney flat-out would cancel the program without a second thought. How many APers go to the parks and never buy a pin or a hot dog or a drink? I see a lot of APers do almost all of their gift shopping at the park. They bring friends and family, they keep interest in the parks up among their acquaintances, they keep the park busy on days when the tourists aren't around.
I love the days we used to get when it was cold and cloudy and the park was virtually empty. But those days also remind me of the days when DL was going through a funding problem, when you could see patched ceilings and chipped paint on dozens of attractions and when nobody was loving the park, least of all its owners.
Attendance=continued operation. It's a simple formula.
I was at DL last Friday, the 16th. It was my son's birthday and we would have attended even if we didn't have APs (or even without the free BD thing) The lot was crowded, the park not as much. Busy, but not headache-inducing busy.
Don't people expect Disneyland to be busy? Don't you think most people would pull in to an empty lot and think to themselves: "so what's wrong with this place, that nobody is showing up anymore?"
So anyway, apologies for rambling here. Bottom line for me is that I think that if we expect the park we love to continue operating, we have to hope (and privately cringe) that the park continues to pull in maximum crowds.
oh...I remember when I was a kid and there was just that one huge open parking lot. Now that was a lot of fun on a hot day!