A reboot won't address it at all (it also keeps you on the same host).. no point in doing that. From the e-mail notification: "You will not be able to stop/start or re-launch instances in order to avoid this maintenance update."
> While executing a stop/start is absolutely fine to do, there is not a guarantee that you will land on an updated host. We are periodically polling for new instances and those impacted will receive new maintenance notifications accordingly.
Which I take to mean there's a chance you could land on an updated host. I'll update if any of those machines come back to the Events view.