There isn't a way to set a threshold alert. I'd just subscribe to an email delivery report or a smart list like you are.
What do you hope to do with this? if you're already blocking bounced records automatically, then all this next step might help you is analyze the list source data.
You got it right! I sometimes have sneaky sources of lead income from far away I want to monitor before it gets problematic. I'm also working on business processes.
Thanks for your input