It’s not just the extra round and (we assume) the extra TV rights funding that comes from it, it’s also money that the SA government has paid the AFL for the right to hold this round. Presumably the government thinks it will generate tourist dollars but time will tell.
Fortunately for the AFL it had at least two states bidding for the round (SA and NSW) so it would be reasonable to suggest that any decrease in attendances and associated ticketing incoming will be offset by the SA governments funding.
As someone else mentioned, it would be nice to think that some of this additional funding would flow down to grassroots footy clubs that produce AFL players while barely surviving on the back of local volunteers and some sausage sizzles. .... wishful thinking.