I've done an awful lot of reading on this subject over the years and have also come away without a definitive answer. Seems to be a 50/50 split of opinions.
However, knowing that new fluid has a detergent effect, it makes too much sense (to me) to avoid doing a complete change on a high mileage vehicle. I'm afraid of a piece of gunk breaking off and creating problems by lodging in a valve orifice. An AT is just too sensitive to that.
But, I'm old school. I'd much rather do the changes every 60K or go with partial changes at higher mileages. Is it overkill? Perhaps. But I tend to keep my vehicles a long time and it helps me sleep a little better.