This was worth doing. As nice as it is to jump into a game, being able to target a friend or family member is great too, especially when you start playing the game early on.
After some testing, I'm not certain whether some of the faults are due to my code, Game Center sandbox environment or excessive concurrent testing and immediate retesting, however for the majority of time, all is well.
I still have some scenarios that absolutely don't work such as receiving an invite that launches the game - looks like there is an attempt to interact with GC before authentication has occurred. All of this will be worked out.
I actually don't use GC for in-game event transmission, just the matchmaking piece. This means I do carry the cost to host networked games but that's ok.
As I support other platforms, this feature can be the native game social hub. Next step is to finalise the menu controls and build a solid state machine to manage its animations.