Hi Shaman,
you might want to check Altona station. There is a plaza outside where buskers get a good audience, there are cafés and a big shopping area, so you have people sitting and passing by. I am a baloon twister by busking profession, and though I've never tried that place myself, I think that it is quite a good spot. If you go there and can't find the place, ask for "Mercado" (the big mall), people will point you in the right [lexicon]direction[/lexicon] and you will instantly recognize the spot I've got in mind.

cheers,
Tom