Also, have you considered using i3 instances for their superior price per throughput/IOP? Obviously, you can't rely on EBS snapshot based backup/restore workflows on those instances, but maybe the performance gain is compelling enough to make the exercise worthwhile?
I have rejected this on the basis that stopping and starting an instance is too useful for solving problems. Even with a few striped EBS disks, instance issues solvable by re-attaching the disks via stop/start are probably ten to one hundred times more likely to occur than a disk failure.
Still, I know some people do things this way, relying on archives and HA for redundancy, and it can be pretty good.
