I am not an expert with regard to WDW in any way, however, I do believe the "trickle down" would most likely take longer to reach them as many people book so far in advance and pay on those vacations over the year. The Q4 earnings probably were salvaged a bit by this plus it seems WDW has been adjusting to the economy in little ways for a while now. Over the coming year, I would imagine those who book and pay up front will most likely still go, however, the number of people who normally book their Disney vacation just prior to it using credit will miost likely decrease.
People want to vacation even in a bad economy. Some will make many sacrifices in order to keep their vacations, others may go regardless and some will cancel anad wait out the economy.
I will say we did just cancel our trip and I was REALLY looking forward to it. There are other things I want to do this year but couldn't justify WDW AND another vacation. hopefully it is just postponed and we will still go at some point this year.
Again, I am not an expert of any sort - just my opinion