Agree on beating the boat after Fantasmic! We walked by as they were loading what appeared to be a very crowded boat after Fantasmic. We made it to Luna Park before the first boat they boarded caught up with us. I can't even imagine how long the people in the back of the line waiting for boats waited. Definitely worth the walk!
We have also driven to MGM from BWV and were able to get home quickly after Fantasmic as well. The trams that take people to the parking lot move very quickly, and the traffic doesn't seem to get backed up in the parking lot either. I personally would prefer the walk, but it's not practical with kids that are too big for a stroller but too young to have much stamina. They'd whine about walking but don't mind at all if we spend 2x the time riding trams around a parking lot....for some reason, that's fun!