I think the dynamic UI layout is more for the iPhone 5 which based on rumours will be longer than the current iPhone e.g. 320x600. The iPad Mini is expected to be 1024x768 so all iPad apps will work without any changes needed.
AppCode is definitely much better than XCode. I'm using it right now, in fact! Jetbrains has done a great job with it.
But IntellIJ is still much more powerful. It's much much easier to build really powerful refactoring tools for a language like Java than it is for Obj-C.
I think the dynamic UI layout is more for the iPhone 5 which based on rumours will be longer than the current iPhone e.g. 320x600. The iPad Mini is expected to be 1024x768 so all iPad apps will work without any changes needed.