It's full of awesome people...*not biased in the least*

Personally I'd definitely recommend hiring a car as there's a lot of really cool stuff that's not available by PT. Definite favourites are Freo, Swan Valley is good (mmm, chocolate factory!) and Whiteman Park for the kiddies - has steam train rides and loads of space, plus there's Caversham Wildlife park where they can feed kangaroos and so on. A cruise down the river is a good way to spend an afternoon in April, not too hot and not too cold. If you're super lucky you might even see the river dolphins.

AQWA I would say is a bit of a gyp these days, $75 for a family and only takes about an hour or so to see everything. Hillarys Boat Harbour is lovely though, plenty of nifty shops, nice restaurants/cafes and a lovely calm sheltered beach for the kids. Water temps might be a bit lower than we like, but DD often still swims throughout April without freezing her butt off.