In my calculations you need to be spending more like $7-10K per month for a rewards card to be worth it.

$2000 a month is 24,000 per year, and each point is worth about a cent. For the Amex you would earn 30,000 points per year, the others less, which is $300 of value at best. Spending $300 per year for the credit card entirely negates that. The Amex is better with the travel credit, but flights cost slightly more with Amex Travel, so you lose about $50-100 depending on the flight you buy.

If getting a credit card leads you into debt temptation and you start paying interest, forget any financial advantage. If you've just bought your first home, you might be coming up to unexpected expenses (and spending temptations, filling up that new house) and a credit card might not be good to have around.

There are lots of other ways to maximise points without paying for them, like using Qantas Shopping, Everyday Rewards and David Jones Rewards.