For having been 11 in the Summer of '76, I didn't, and I don't know why. I should've asked Dad while he was alive, but it never crossed my mind. I mean, we hit up Expo '74 in Spokane, WA, and as big of a train fan Dad was, we just didn't go to see it when it arrived in Seattle around two years later.
There is a historical website for the 1975-76 AFT (https://www.freedomtrain.org/main.htm). I looked at the schedule for it through the Pacific Northwest, and we could have gone to see it, there was plenty of time, and as it would have rolled through Everett on the BN mainline between Spokane and Seattle, we could've also railfanned its movement.