Funnily enough I did start looking at the APIs to see whether there was anything I could cobble together quickly from it. The batch API looks like it will let me pull data out en-masse but in a somewhat clunky fashion, and the REST API looks like it's potentially additional cost!
As I've got the luxury of direct database access, I'm probably going to just grab data directly from the tables and either create something in PowerShell to do the grunt work, or possibly a go down the route of creating a web-app of some description so I / other teams have more visibility and control over what has been / is sent.
Interestingly, the school took the decision to move away from the parent portal in favour of using My School Portal. Inevitably we gained some additional functionality but also lost a fair bit too. We've got all the email templates set up, but as with any process, remembering to do something is always the weakest link!
Having previously worked at a college where we extensively used data based triggers in the MIS system to initiate workflows or generate SMS or Emails, I can't help but desperately miss not having similar functionality in iSAMS. I guess I've just been spoilt!