Thanks for the help, kwag.
I tried both of those filters, but unfortunately I haven't had much luck with them. But you definitely put me on the right track with avisynth filters instead of VDub filters. I checked into avisynth filters and finally found convolution3d, which in conjunction with VDub's internal temporal smoother, seems to do a pretty fair job. It's not perfect, but it works.
Temporal smoother at full power will clean the defect perfectly, but I get a lot of really nasty ghosting artifacts at that power and some of the motion looks unnatural, so I'm not prepared to make that trade-off just yet. Do you know of another filter that will do the same thing without the ghosting?
rendalunit: Thanks for the tip. Fortunately, this problem is now several years in my past, since I now have DirecTV and have no problems with video quality.