Really the main added benefit for your 2x$200 is checked bags I think, so it depends on the nature of your trip. You can use the hand baggage allowance which although not stellar is ok for a short trip. The answer to your question really is to work out what luggage you might want to bring and take home with you, look at the price for adding that on the basic fare, and compare with $400 to see whether it's worthwhile.