For me personally, I do pan drops and change the filter everytime. The reason is that it is cheaper than paying a garage to flush/fluid exchange by doing it myself. Plus I get the satisfaction of knowing the filter was changed as well (you don't change your engine oil and leave the old filter on there, do ya). So that is what I would recommend.
If you cannot, or do not want to do your own work, then by all means have the fluid exchanged out. But don't overlook the fact that the tranny filter still needs changed at some point.
