I am going to be in Perth for a week around then and am looking for some interesting things to do. Perth is a great place but I don't see enough of its culture so a good festival or such would be fun. Even if it is just something that revolves around food or such...
Firstly, remember it's cool/cold in Perth in July BUT there is still loads to see and do. Take a walk on Cottesloe Beach (it'll probably be sunny) and experience the waves and great sand, try a day trip to Rotto when it'll be less busy than usual. The bays are quite fantastic and special, a bit like the Greek Islands (yes I know, but it's true) Check out kings Park in the winter - it's really neat in the rain !
Above all, don't sit in your hotel room if it's cool, get out there and experience Perth's environs - look at the visitors guide and pick something different ! about 10 years ago