Two thoughts on possibly adding to this I've had:
1) a corresponding 'SendMeTopic' command, to do the same for a whole topic (either as individual e-mails, or some sort of summary or digest)
2) a command - either via e-mail or web - which would probably need to be available only to (selected) moderators (e.g. 'mentors' mentioned above) - to send a specified message or topic to a specified member.
Also - a thought which occurs to me - would an (e-mail) command to send a suitably tailored link (could this be set up to obviate any need to deliberately logon, by use of the same sort of 'logon token' involved in the logon by e-mail process?) for a member to go straight into the relevant message or topic webpage avoid some of the issues people see with e-mailing old messages, while meeting the identified need?
And I can see the desirability of being able to tailor the availability of any of these at a group level.