My idea's.. Ill take a shot since I never been on a cruise. I don't exactly know what certain requirements or preferred places but here it goes.
1st Suggestion - Follow the coast line? Head through Cottesloe 30+ ish day and head down through fremantle for a stop somewhere (Fish and chip place next to the ocean, forgot the place name). I haven't exactly thought it out perfectly but I know that Fremantle has nice scenery and Cottesloe; I drove down there in my car once I had was stares.
2nd suggestion - I would say a highway cruise into Joondulup and go into the Joondulup Resort (Stops on the way not sure). I been there for a wedding, very nice location and all roads aren't narrow and tight, open highway. I know Chase_D likes to avoid highways and major things but a great look at scenery and nice weather.
Overall: Joondulup might be far for most and may not even have the day to do, I am just thinking nice locations and scenery. I wouldn't want to cruise into Ghetto or urban area's. Clean built up area's and something nice to look at. I think while we have such hot days lately lets try and use them. We all have lovely MR2's ranging from the slightest thing, I don't think most of you (I hope) want to cruise into things like industrial area's and all that.
That's my opinion on a cruise should be about being able to look and scenery enjoy the air and your car and the group for MR2's. (Might sound fruity) That's how I think of it anyway.