It depends. If you are planning on flying with SW in the future, you could book now and when (or if) a Ding! comes out you can cancel your full fare ticket and rebook at the Ding! fare. Not all of SW fares are refundable, but they will give you a credit to use on a future flight. They do not charge anything for changing the ticket. I can speak from experience that it can be hit or miss with Dings!. I have been waiting forever for a Ding! from PHL to MCO to no avail. They seem to have disappeared off the map.
You can sign up for the weekly specials at www.southwest.com. There are sometimes great deals thru there and also thru the internet only specials.