Here's my list:
Wave Rock: Just a big stone skate ramp, enough said. I guess the only reason I'd recommend a tourist to come out is if they wanna see a bit of the wheatbelt.
Pinnacles: They're a lot shorter than you think, but I guess they're pretty unique. I would say maybe slightly overrated, but I guess Perth lacks truly amazing sights we have to promote what we've got.
Dunsborough: Not sure much an attraction per se, but the town itself has become just a slice of suburbia in the Southwest. At least I can say the beaches surrounding are still great for surf and just having a swim.
Broome: Sad to say but I found the town a bit overrated. I like laid back, but Broome is a lot smaller than I thought. Most Perthites don't make the trip (I visited on a round Oz trip) because of distance/price. They'd rather visit Bali. Cable Beach is nice, and the Kimberley is the real outback but Broome itself is nothing special.