I was able to get the ME firmware to update by uninstalling it from Device Manager and rebooting (twice) without uninstalling the busted System Aggregator entry (it seems if you uninstall both it tries to do the SA first then fails and gives up).
However, even with the ME updated, I still can't get the SA update to succeed. It starts with a small amount of the progress bar filled, then ~30 seconds later gives up.
I also tried installing the MSI (downloaded today) and it didn't help.