Eels give kids free memberships with adult GA sold and Storm give registered vic payers 3 game memberships. Panthers apparently give out thousands of free tickets every game to registered Jnrs and no doubt some other clubs are doing similar promotional activities.
No problem at all with that, great marketing strategies to get people into the habit of going to games. But it is an example of how number of members does not always equate significant revenue. At least to start with unless they can then get converted to full paying memberships.
And bringing it back on point, that's the beauty of having a 30k stadium. It means you can do all sorts of marketing strategies to fill it when you have redundant capacity, like free or very cheap kids tickets, reciprocal game membership agreements with other clubs, bring a friend for $5 deals etc. If your stadium is 15-20k you dont, or bloody well shouldn't!, have the capacity to be able to do those sorts of deals.