Well, I visited Swanbourne yesterday for the first time in quite a few years and it is definitely not as I remembered it. Despite the 40 degree plus heat there were fewer than 40 people there and, for the most part, they were of my vintage (ie a bit past 50) with the leathery skin and saggy bits that go with a lifetime of cooking oneself on beaches. No sign of the younger hotties or even the gay couples who used to be regulars there and even the kiosk is now closed.
Cottesloe was pretty much the same again - carparks were full but probably more people in the pubs than on the beach. I believe the great Aussie beachgoing tradition is on the way out - probably too many other more interesting things for young people to do these days.