I disagree. I think small stadiums automatically limit the number of people who consider going to the game. A crowd of 15,000-ish in a 20,000 seat stadium is typical - it would be highly unlikely in Sydney to have complete sell outs week in week out. However, play in big, easy to access stadiums, with seemingly limitless seats and plenty of cover - most decent Sydney clubs would grow their figures (in line with performances of course). Big venues encourage the spur of the moment "let's go to the footy tonight" scenario.
We should aim for big blockbuster games getting 40 - 50,000. It will take time, but once that culture is established it'll stay, people won't think about going, they just will. Crowds won't / can't grow much more in current suburban grounds.
Either upgrade grounds to 30k (who pays for that!), rationalise grounds and upgrade what's left (middle of the road) or go down the AFL path.