The colosseum would be great center for open PvP: You can pay for admission, walk in like nothing just to see everyone in the arena hacking and slashing and casting spells at each other...

While that time, the place would look empty and gradually start filling up with audience before the main event begins.

I don't think casual PvP should be rewarding but everyone should be giving a phoenix down to raise fallen PCs or else HP to the nearest crystal. Lol, mindblowing idea would be that the main even would be pre-registered PCs from different servers to battle on another. The prize would be accomplishments and trophies plus exp and anima.