I think this thread has shown the ever changing climate of air services to regional centres in Australia. In the last 15 years the BNE-TNG has had the following aircraft types;
Metro 2, Bandit, B200, Shorts 360, E120, J32 , then back to the Bandit and now a Metro 3. At one point both Flight West and Sunstate were flying the route. In the early- mid 90's Sunstate overnighted a 360 at TNG.
Small regional centres all over Australia are facing a decline in Air Services. The larger Regional Airlines have moved up to larger 30+ seat aircraft and the towns that these airlines once flew to cannot support the larger aircraft. In NSW many towns that once had turboprop equipment now only have a PA31 or no service.
The BNE - TNG is currently a stand alone route so it cannot support a 30+ seat aircraft. If it was linked with another town, such as BLK, GLD or BUD then it might required a larger aircraft such as a 360.
I think most would agree the Bandit does have a slight edge of the Metro with regard to passenger appeal, but the Bandit lacks range. The SEA Bandits are fitted with 15 leather seats. These seats are heavier than the old 1 + 2 bench seat that most Bandits have. The operating weights of the SEA Bandits are around 150-200 kg higher than those Bandits fitted with the standard seats. The Bandit on this run is limited to no more than about 14 passengers on a good day. The Metro on the other hand can carry 19 passengers on a bad day. The passengers may not like the Metro but it is better than no service at all.
This Metro is owned by SEA's parent company Aeromil (ie no purchase cost to SEA). I'm sure if they owned another Shorts or a Bras then they would have tried to use them on this route.
The B1900D has also been mentioned on this thread. Yes it does have the best passenger appeal out of all the 15-19 seat aircraft and yes it is expensive, but you are getting a very versatile aircraft. The B1900D has some very good gear up the front, 99% of the passengers can stand up in it, you can carry a small bag on with you plus it can carry 19 passengers fly for around 2-3 hours with reserves. The Dash 8 is the same, it is the most expensive of the 30+ seat aircraft but it is versatile. The B1900D needs to be doing more than 2000 hours flying per year otherwise you are in trouble. Unfortunately SEA do not have enough routes to make the 2000+ hours per year.