QLD defect notice is 1 demerit point and a fine. Used to be $75 but it has gone up.
Any aftermarket bonnet or panel on a car is illegal in QLD if it does not have a ADR Approval type certificate. I believe they do need to undergo crash testing etc to be compliant. Carbon fibre ones just seem easier to spot by police, therefore they are targeted.
There is, however, only one bonnet that is legal which is by the company called BLITS. They are in Southport, Gold Coast somewhere if I'm not mistaken. But as stated they only make fibreglass ones at this stage.
Only way to make your bonnet legal is to have it crash tested and approved.
Having said that, a carbon fibre bonnet won't pass a roadworthy certificate inspection either.