Well heres the AAL height limits map. Now, the trajectory of all flight paths is directly over North Adelaide (the big band with the 120/130/140 markings) on it. What I don't understand is why a deviation has been allowed for the southern side (closer to the CBD) with the 140/153.5 markings and none for the northern approach?
Having experienced landing from the airports NE-SW runway alignment, approach over the city, planes usually finishes deviating the hills (from Melbourne or Sydney) and begins aligning straight somewhere over Holden Hill, where it begins its descent to the runway. This could be the reason why the southern deviation has been set aside for late incoming planes who need further time to re-align into the runway path (as they are coming from the southern index).
IMO, regulations should be changed to declare the city a no-fly zone, and the southern deviant reversed to the north. Melbourne/Sydney inbound planes are able to land on the shorter runway from the SE/NW alignment. (But they can't take off on the same length). My proposal would be that all MEL/SYD flights taking off goes to the SW to circle the city from the south, and land from the SE or SW. Brisbane/Darwin/International flights should be able to take off to the NE, however, since they fly north, their approach and take-off would come in from a more northerly direction (hence why I propose reversing the deviations) so they align away and into the current runway alignment. Perth flights would be unaffected as they can land from the NW on the shorter alignment or, takeoff/land from the SW alignment. Other international flights to the west can just takeoff as per usual to the SW.
As for SYD/MEL flights, it could help if they extend the SE/NW runway to the vacant land across Tapleys Hill Road so takeoffs are possible using that alignment to the SE. However, I think this could be possibly hindered by the Burbridge Industrial Park development? Digging to the past, It could really have helped us now if they built the parallel runway on the SW/NE axis whilst they had the land to do so, same applies for the SE/NW runway extension (you can see the land reserved for that in your street directories)
Amongst all of this, It could help in some way or another to relax the height limits in the CBD.
There's bound to be a flaw, or several - so feel free to justify any mistakes.