Same here.
I have learned the same things you have about their overhead and other numbers. I drop a dollar in the bucket when I go by. When the kids were little, I'd give them each a bill and let them do it. I also write a check now and then.
It's only during the holiday season, the volunteers at the buckets are almost always good-natured and a pleasure to talk to, and I find the bell-ringing uplifting myself.