> a "1990s style mailing list" isn't going to increase your visibility enough to get hired

This is too limited thinking. I can't tell you what the opportunity will be, but there are opportunities if you participate pro-actively, even if you think of opportunities only as job opportunities. In percent it's probably smaller than in 1990, but in absolute numbers it has grown just like every other market around the internet and IT.

> there is a third category

Completely agreeing with that part. To some degree they are also part of these people who don't really use the internet. If you just scroll through your facebook feed and click like here and there, you are not participating. You must at least be able to answer most daily questions via google to be considered participating.