I second the notion of going to Cottesloe or Fremantle. Cottesloe is a sleepy little beach town where I have stayed in rental flats. Beaches are great. Some nice places to eat.

Freo is much more lively and developed mainly for tourism starting from the time of the Americas Cup races some years back. Fun. Not too big.

Perth city center is a bit dead. On the river as mentioned, overlooking "Perth Waters" which is the big ballooning of the river. Home of the Royal Perth Yacht Club, former holder of the Americas Cup. Lots of sailing. No beaches to speak of.

Great trips to the south. The wine country of Margaret River. Good B&B's some excellent vineyards and restaurants that go with fine wines. Near caves.

I have spent a good bit of time anchored off Rottnest, but not much time on the populated part of the Island. There are great secluded beaches on the west side and some decent but not spectacular snorkeling and fishing.

Good place, WA!!!!