I think mailing lists are important because it's a direct line from you to your fans, not dependent on a third party like a social media platform where things might get shut down or your posts might get lost in the update feed. Also, if people have gone to the trouble to subscribe to a mailing list, they're probably enough of a fan of your work to be interested in learning more about/supporting your projects.
I have a newsletter for my other illustration projects (I've done a coloring book and a children's book on Kickstarter and have a several hundred address mailing list from that) and when I recently plugged my Webcomic Patreon to that mailing list, I immediately got a couple of patrons who were fans of my other work.
I'm planning to start a mailing list specifically for Imaginarium with a sign-up page through mailchimp. I'll offer some incentive (immediately get a free wallpaper!--something like that) for joining the mailing list, then only send out emails when there's something big to announce (Kickstarter, new project, etc.)
Incidentally, if any of you DO have a mailing list, what are the incentives you've used to encourage signups? I don't know if the Spaceboy creator is building a list this way, but I know in the past he had a printable paper figures set of his characters available...that could be a fun incentive, too. Hmm... after I rebuild my 2019 buffer I'll have to give it some thought... 