Dave,
SS can't be our 3rd tier. Why? Because it's only Sydney and Waratahs players. Logistically it only can and should be. The top 175 players are contracted. There are 180 starting players in the Shute Shield every weekend. Roughly the same in Brisbane, Canberra, Perth and Melbourne.
That means for the 9 players (Based on 2015 squads of 32) that aren't in the 23, and let's say the next 32 players who are in the hunt in each city, they are playing in a competition where the majority of players are well below their level. They are not being challenged adequately and aren't being tested for the next level properly.
That's 45 contracted players, 175 potential players playing in a pool of roughly 800-900 players. Imagine the drop in quality from these 175 to number 800 on that list? I've played Dewar Shield in Melbourne - I reckon I'd be about 800 on that list. Players aren't preparing themselves for professional rugby running rings around me on a Saturday.
Rebels and Force shouldn't be expected to send players back. Firstly there's a costs, secondly they cannot logistically monitor the players progress and thirdly, there is the injury management issue which is why the Brumbies moved all their players to the JID. It's also short sighted and poor for the game and clubs long term to be parachuting players in that do not contribute to their clubs otherwise.
The NRC means that these players each weekend are playing against a pool of the players that are ranked 24 to 230 of those who are fit and available in Australia. Players will develop to Super Rugby standard better by being challenged further and will also be adequately tested to determine if they are closer to Super Rugby standard.
Look at JJ Tualagi from the Reds. Was a standout in premier rugby in 2013, looked woeful at Super Rugby level in 2014. Why? Because there is such a large gap in the standard.
Even if every player in Australia player Shute Shield (just a hypothetical, why should NSW rugby and SS clubs get the benefit out of all of Australian rugby), that's still 3 more teams and talent spread thinner.