Yes. Our airfare went down and they gave me a credit of $108 for future travel. Haven't used it yet, but I'm working a plan to go back to WDW in September and will use that $108 toward the cost of air travel.
Yup, just got my $30 credit last week. The airfare for our free DDP trip in September had a web special. I called and within a few minutes, voila a $30 credit! Well worth the phone call.