Hey guys well firstly being from WA i dont have intimate knowledge of the coastline over there, other than from my readings and from the 2 times ive being over there. So here goes.
Firstly the southern Goldy points get there sand from the southern rivers like the Tweed which pump out a fair bit of sediment. This available sediment combined with the dominant S/SE winds and current help push the sediment up and around the points, and deposit them out along those perfect banks that make up the super bank. So as long as those rivers keep flowing and those SE lows keep forming and pushing up along the coast, the Goldy points will always have banks. (Climate change, reduction in rainfall, removal of sediment from the river etc could all have an affect on this over time but i will talk about that another time.)
As for the beaches up around Surfers, well thats a different thing altogether. The whole Gold Coast is pretty much an island of sand (Pacific on the east, Canals and rivers on the West) so is a very dynamic area that is constantly changing and moving around under the affects of waves, currents and wind.
Before development, the Gold Coast would have shown a very different coastline each day. Beaches would have moved a great deal more than they do today. In a general beach cycle, sediment is cycled from onshore (beach/dunes) to offshore (banks) and back again. So back then there would have been a great deal more movement in sand from the beaches into the ocean and vice-versa.
Since development, the amount of sediment available to the beach cycle has reduced a great deal. Compared with what there would have been prior to development, there is really "no" sediment for the beach to cycle. So there has been a reduction in the amount of sand available to make sand banks, hence why there may appear to be less quality surf banks. As the development increases along that bit of coast, the sediment available to the beaches will only reduce more (unless there is beach nourishment, which is a fix of the symptoms, not the cause).
The high rises along the Goldy have also have changed the local winds. For example, when i was there in April, the wind was fresh out of the South. When i went for a walk through Surfers i noticed that the flags along some of the roads were showing the wind blowing direct West, while a bit further down the road another showed it blowing from the East. This just shows that the buildings have caused the winds to move around in between them. This may have an affect on the position and quality of sand banks adjacent to high rises. A southerly wind is one that should be moving around the sediment & shaping the banks, but if at certain parts along the beach, the wind is blowing in a Westerly direction then the banks may not be shifted around.
Cal, I hope that answers your question a bit. It would be very interesting to have conducted a study into local wind patterns before development and compare them with local wind patterns now.