If you use the onscreen display for lights, security, heating etc then don't upgrade as you loose all of this. The benefits are not enough for me for the loss of functionality.
The only hardware I had thats not supported was the touchscreen, but the new app on an iPad is far better.
On the plus side the new app is very good, lots of nice things like being able to see which lights are still on, rather than having to scroll the whole house to find them. Also putting shortcuts to things on the main screen are very useful.
I've not found any exciting functionality that makes it a must have, but apart from the OSD stuff thats missing its much nicer to have.