I don't totally disagree with you except I see none of those locations you mention as safer from the CSK's point of view to take the victims. I have often wondered "why Claremont" and I couldn't really put faith in the theories about him " having it in for the upper class" or "working at UWA" etc. I think the link with the KK rape victim puts Karrakatta squarely in focus for the murder location for all three missing/murdered victims and the reason he struck in nearby Claremont.
The first reason KK stands out as the location he took the victims is Familiarity. He'd been there before (allegedly) and had been successful in getting away with it. The location wasn't risky, but the 'leaving the victim alive there' part was.
Secondly, the chance of disturbance. I would say, beaches and river foreshores are poor choices because of fishermen (as you said) and some who like to go down there at night for odd reasons. People also often pull in to beach carparks to 'get high' before going to bed for the night or, if they'd "pulled" for the night, they'd park up for a bit of action. UWA, Kings Park would be out of the question IMO on this basis and the parks also had the risk of possible night functions e.g. hired them for parties etc.
Thirdly I would say the distance from the pickup location would have been very important. In a station wagon, as I said in a previous post, he would be very paranoid to be pulled over by the police with a living, moving victim. If the police pulled him over, it'd be hard to conceal a moving body in the back. KK is just a few backstreets away from the pickup location, unlike other locations you mentioned, such as the beaches, it's hard to see them being more convenient than KK.
Fourthly, Ease of access/exit. With numerous entrances, it could be conceived to be an ideal place because, unlike others there's plenty of entries he can take. If he was nervous because he'd had a car drive past on one occasion near, let's say Government rd entrance he could always pull around to the Smythe Rd entrance or Railway Rd.
Lastly I'd put the risk of the vehicle being spotted while parked in the mind of the CSK. McGilvray Park and other locations, while most likely very quiet at night, may have had the odd car driving nearby or the perceived risk in the CSK's mind. Assuming he's killing them there, the location would have to be one where the car can be parked out of any potential sight.
Overall I think the key factor here is, assuming the KK rape was done by the CSK, the familiarity and success he'd had there makes this the obvious choice for him over new, untested locations. I would suspect if he'd used another location it would have been because he got spooked on the way to KK and had to find an alternative.
