My guess is that the 'smoothing' effect of old dirty trans fluid on hard shifting is the source of the paranoia about flushing old transmissions. Your advice as well as others has been extremely informative. Absolutely no one I have talked to in person, weather auto shop employee, parts store worker or layman has given me any information as satisfying as this.

The best thing to do seems to be what you and a couple of others have suggested: do a flush first with cheap regular fluid and then another flush a couple of thousand miles later with synthetic.

Thanks!