ABC Rural had a recent story about planting more humas in the soil to increase cloud seeding to try to increase rainfall. The conclusion of the story is correct, most of the organic spores will be blown downwind and not effect the local area they were produced in. There are many possible sources for rain particle nucleus it is near impossible to map the sources to get any clear picture on which source creates which raindrop.
Cloud Seeding for crops has been going on the last 55 years in western North Dakota. Their 2013 report has shown a increase in crop quality in the areas downwind of where clouds were seeded by airplanes during the growing seasons. The 2014 report should be out soon. Seeding like this has added $5.41 to $8.41 increase per acre in crops grown.
So while planned cloud seeding at altitude has shown a meaningful effect, planting humas at the boundary level will not have the same effect in Australia.
Scheduled cloud seeding like in North Dakota can be taken to the next level to study the effects after September 2015 with low level UAV scans, both imagery and LiDAR (remote sensed or derived). This technique can start right now in Australia with their current UAV laws, you just need a license to fly it.