I very much 
this idea from @awesomerobot.
Also thinking generally that a simple export tool in admin might solve most of these cases to help admins manage their users - e.g. export to CSV a list of all users that can then be imported into another tool. For my community, I use another open source tool called CiviCRM for relationship management, send out newsletters and other membership related tasks. CiviCRM has a pretty awesome data import procedure.
Another approach might simply be to use SSO with another web app that handles newsletters etc so that this info is captured in the other tool already and is always up to date and ready to be used.