You already have alerts and images (snapshots/backups), now all you have to do, is setup some config that when XYZ alert goes off (80% CPU) auto spin up a new droplet (size determined by config) and attach that to the load balancer. This Droplet would start accepting traffic once the health check passes.
As a phase 2, when certain alerts get hit (cpu below 20% for 60 minutes), then de-scale by killing off the youngest droplet.
It seems like all the pieces of the puzzle are there, and it appears that nobody has asked for this specifically like this before on here. Please correct me if I'm wrong.