1. Python is a good language to learn. You can use it for other things beside building a web app. GAE is similar to Django.
2. The GAE datastore is easier to fathom than a traditional database. For some reason, I always found databases hard to understand, and it seems that designing schemas for non trivial projects is a separate and distinct skill set from software engineering.
3. GAE solves the updating/patching of working code by providing a sane environment and tools to update and version your app. You can easily switch back to a previous version. Patching datastore schemas is slightly harder.
4. You get scalability out of the box. You don't have to worry about hardware, or even configuring "virtual" instances. None of that. But you probably won't have to worry about scalability for a while.
5. You can easily deploy code to multiple environments. You just need to signup for more apps, and update your app.yaml file to point to a new app name. You can do this in a simple build script.
I hope this helps.
Cheers.