Dick,
1. Just because they do it in the US does not make it better or safer. The US has far higher terrain and as such MSAs - in some cases necessitating flight above A100 - we don't. The physiological aspects of operating for extended periods with a cabin alt of over A100 must be considered and IMHO not worth the increase in risk in Australia.
2. It is my understanding that the requirement for rejoin via a 5nm final is for licenced airfields only and therefore your example of a farmer & paddock or a crop-duster (unless it is at a licenced field) is erroneous. Given the frequency of most recreational pilots flying I would think it prudent to maintain this requirement so as to facilitate identification of all circuit traffic especially now that you have allowed non-radio equipped aircraft to operate.
Perhaps you might look at how CASA can justify charging $130 (soon to become $75) to process medical licences for those without restrictions ie. no thinking required. Even at $75 this is ridiculously expensive.