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"joke" probably overstates it but Elizabeth Quay is a multi million dollar development in the heart of Perth that involves removal of a large park to be replaced by river and various public open spaces. It has been controversial as it's largely taxpayer funded at a time of budget stringency with the China downturn. It opened a couple of weeks ago and the general reaction has been that it's a bit underwhelming - I think it looks a bit Singapore but be sure to come and see it for yourself.
In terms of your suggestions, I personally think the dolphins are overrated but depends how keen you are on them (if you spend enough time near the Swan River you are pretty certain to see some) and Shark Bay is quite a hike off the North Coast Highway so it's not really a brief diversion. The scenery though is stunning - red earth, white beaches and acquamarine water and some interesting history plus the fun of visiting somewhere called "Useless Loop". The great thing about Ningaloo is how close the coral is to the shore, you swim off the beach and there it is. There are various kayak tours which take you out to the fringing reef where you'll probably see (small) reef sharks and turtles. Food though is expensive up there so if you are driving stock up in Perth if you have room and intend to self cater.
