I know that there are loads of stuff to do after the Elite Four, and I'll list what I've done. I'm not positive if there are more:
I'm getting sort of bored with the game a bit. is there something I missed?
If you used Memory Link:
If you are REALLY bored:
Just to tack onto DA's answer.
If you are REALLY, REALLY bored:
Well I think there's two things that you missed:
Have you made some movies at pokestar studios yet? I can find that pretty entertaining.
You can also doo some Join Ave. business. It's fun to upgrade your avenue!
Hope I helped you, Mew:3!