There are Tours of Greece and Bulgaria actually, they're just .2 races, much lower ranking, and not attended by any of the top teams.
As I said, even if you can't shift it around to the other states of Australia (the US example is a better example than Europe, because the European states are independent nations while US states, Aussie states etc are states within a federation), you could at least vary the route around Adelaide; at the moment the parcours is near identical every year. Why not one year have a prologue TT in Adelaide on the crit course and then finish at Willunga? Or just get from the same towns to the same towns by different routes? I keep suggesting (though I know it's probably not viable) an XC-skiing type pursuit where riders are set off on a 15-20km course (perhaps the loop around Willunga?) on their race time so that the GC would be the same as their finish times on that stage. In a short race like the TDU that could be possible, especially if you had a TT. You could do it as a stage 6a and 6b thing, perhaps, with the ITT and the pursuit replacing the criterium.
It's just about shaking things up. The main criticism of the TDU is not about where it is, who rides it, or anything like that; it's that it's dull and repetitive. The organisers don't even have to make it much tougher, just make it at least look like they're trying to address the problems the race has and improve it otherwise it will stagnate.
Edit: I was writing this while you posted your reply above, evidently we're on the same page with this part of the question.