Great suggestions already from everybody!
I would like to add a suggestion for a new core module. I believe that a newsletter module should be added as a core content related module. There should be content hooks for the core modules: news, links, newbb, faq, members, etc. These hooks should tell XOOPS to "place this content, in this location, representing this timeframe".
Thus once you set you your newsletter template, it can be automagically generated by the system and sent out to members who have elected to receive the newsletter.
Also, people should be able to sign up for the newsletter but not membership.
Thanks for listening!