When exactly do you bake a new AMI? On every Soundslice deploy?
Baking a new AMI only happens when there are new underlying dependencies, like a new package from apt-get or a new Python module from pip. In other words, it's rare.
Hope that helps!
I could also change the AMI's "user data" to run pip when the instance loads, but I'm not 100% confident it will always run without errors. I feel better doing it manually and baking it into the AMI. Personal taste.