Ok besides the trophy what prize do I get by collecting every Spirit? Plus what do I get for completeing the flick rush cups. I've already got the Unbound keyblade, is there any stronger?

You get only the trophy from collecting all Spirits. If you complete all cups, you get the Sweet Dream Keyblade.

The Unbound keyblade is the strongest in terms of attack, there's another one that's the strongest in terms of magic which, I think, you get from completing every Special portal. By collecting Spirits and leveling them, you can unlock new abilities for Sora and Riku and also collect new commands like Mega Flare, etc.

 

I'm not sure about beating Flick Rush cups, as I've yet to do that as well.