This suggestion comes from an issue I've noticed in many forums I use that use XenForo.
Say a user profile or thread is reported, and a moderator marks that report as resolved. Later, in three months, a different user reports the same user / thread for a totally different reason, and a staff member chooses to close the report and send an alert to the reporter. Not only will it alert the most recent reporter, but it will also alert the reporter from the past report, regardless of time frame or whether there was a resolution after that first report.
So, my suggestion is to add an option when handling reports to alert all past reporters regardless of whether a report was handled. I believe the default behavior should be to send an alert only to all reporters since the last resolution by a moderator (i.e. either resolved or rejected, not assignments). This would make a less confusing experience for users who are always alerted from reports they have made a significant time in the past, but no longer have a personal attachment to the report.
I think this would be especially useful for medium- and large-sized communities that handle a significant amount of reports on a regular basis.