Unfortunately i've never been to an NRL game
(I live in Canada). My dream is to make it back to Australia (i was there for 6 months, 5 years ago), and check out a SOO game and some club games. So I can't speak on the atmosphere around the grounds for NRL games, but i;ve gone to a few NFL games and College Football games in the US, and there is certaintly NOTHING that tops the atmosphere of a great tailgate.
Toss around the pigskin, bbq some fresh meat, sip some brewskis, play some frisbee, chat with strangers..it just is such an amazing atmosphere, but you really do either need a large car park around the stadium, or a highly residential area with some parks where people could meet and gather.