Let's say the dumper, whoever it may be - suitcase man or no suitcase man - was for some reason heading towards Adelaide/away from Melbourne or some other eastern location...
If someone did happen to be driving back in this direction with a body in their possession and had so far been unable to decide how/when to dump it, it would probably dawn on them right around about Tailem Bend that they were about to arrive in Adelaide and had better quickly dump their load. There is no way anyone would dispose of the suitcase on the main freeway which is extremely busy. They would be sighted immediately. Instead, they would probably and hurriedly opt to turn off the beaten track. It's probably safe to say that the Australian instinct in terms off getting 'of the beaten track' would be to turn inland, not towards the coast. Turning inland at Tailem Bend, of course, takes you to Wynarka.
Something along these lines that I have sometimes wondered ... to the folk of this tiny town the suitcase man appeared utterly conspicuous. But I wonder, would someone from the big smoke, for example, feel conspicuous wondering through a distant, isolated, unremarkable town? Or would they feel like they were in the middle of nowhere and utterly forgettable? I have a feeling I would feel this way: nowhere and nothing, rather than something to be indelibly imprinted on everyone's memory.
Edit: to remove reference to Stephanie Scott case (sorry Makara just read your post to that effect).