I think a number of your are being unnecessarily negative and bordering on rude to this guy. He's fairly new, he's obviously a keen enthusiast and he's putting some actual effort and thought into organising a cruise.
Maybe instead of shooting him down you could either offer a modification to his plan that you would be interested in or just leave it alone.
For what it's worth, I wont be in Sydney that weekend but if I was I would be thinking that it does sound like most of the journey will be in traffic. Maybe try a 3 or 4 pm start heading across the city to the east, maybe some beaches but avoid Bondi, then continue the way you previously thought. Bondi rd on a sunny day barely moves.