What's the difference between IDEA Community Edition and Ultimate?

No, for Android Dev only the UE (Ultimate Edition) it is not probably worth the money. The CE (Community Edition) supplies you with most (if not all) what you actually need to develop a real-world Android project.

IntelliJ IDEA Ultimate Edition is very much worth his money if you have to use it for a wider spectrum of languages/frameworks/projects.

Have a look at the comparative table here:

http://www.jetbrains.com/idea/features/editions_comparison_matrix.html?IC

As you can see, if you have to use it for web development, or in an enterprise-level environement, you will have to buy the UE. For Java/Android only, the UE is quite an overkill.

Community Edition: open source and available free of charge. The Community Edition is covered by the Apache 2.0 license, and is built together with the open community around jetbrains.org.

Ultimate Edition: professional and fully-featured commercial IDE provided by JetBrains. The Ultimate Edition is built on top of the Community Edition with many extra features for web and enterprise development. You can download IntelliJ IDEA Ultimate from http://www.jetbrains.com/idea. You can evaluate it for free for 30 days, purchase a license, or get a free license if you're a contributor to an established open-source project.