Recovering iWork from backup
You also need to recover library files:
/Library/Application Support/iWork'09
/Library/Preferences/com.apple.iWork09.installer.plist
/Library/Preferences/com.apple.iWork09.plist
In my case, this was the minimum requirement to get Keynote starting again.
Additionally, you might want to recover user-specific files from your user directory:
~/Library/Application Support/iWork
~/Library/Preferences/com.apple.iWork.*