Gidday Vic, and welcome.
Don't be nervous- your point is very valid. The "idiot" is the one who does not ask the question.
If you buy a block, and you put the house on it yourself, you will probably save a fair amount in stamp duty. No question (though if you bought Off the Plan, in some states, you still pay the stamp duty).
If you developed and got it built yourself, you have the potential for also saving a lot of money- probably heaps more than the stamps you would save.
I'm not sure about buying a house and land package.
But always be careful that you are creating something for which there will be a demand.
If the land you are buying is in a new area, with lots of land available, for instance, there migyt not be any capital appreciation for some years. But if it's in an existing area, with lots of houses already, you'll get heaps of appreciation immediately.
You've identified one factor- one which many will have missed. Well done.
There are other factors which may affect your investment.