I've received a fair number of replies to my inquiry about mail volume. Here are my conclusions. There are a fair number of people who do in fact have problems with mail volume. There are lots of us who don't, but I think that as a matter of courtesy we try respect the needs of the entire list. Some people just don't like digests, some can't undigestify them.
Most people seem to like the idea of people voluntarily restricting their mail.
The problem here is individual cooperation. I personally like the idea of people voluntarily reducing their output. I am willing to meet them halfway by collecting all all inquiries and batch-mailing them to the list, say, every week. They won't be in digest format, so you'll just have to look through them somehow if you want to answer questions. This is very thoughtless.