I'd expect that it has very little to do with posturing or spending. The airlines will go where the passengers are...they can't afford 'build it, and they will come'. Not for long, anyway.
I know what you're saying: the airlines are not government or franchised bus, ferry, tram or train operators that are subject to politics, are often heavily subsidised, have a community service obligation and can increase frequencies at a politician's whim. There is, however, an element of inducing additional passenger numbers provided the required population density is present. I am assuming that the economy is in reasonable shape and does not crash.
Initiatives such as turning a three days a week frequency into a daily frequency can increase passenger journeys, as can providing say three trips a day instead of two each way. If this was not so, then frequencies on many Australian domestic air routes would have remained stagnant.
It is complicated a bit by some states offering airlines subsidies for intrastate routes, especially prevalent in Queensland.
It might also depend upon whether other airports are close and whether driving or using trains is a substitute, and the relative cost of each mode versus time.
Most of us prefer to live near the coast so I wouldn't have though Tamworth is likely to increase much in population in the next few years, apart from the usual pattern of soaking up residents from small nearby towns as the latter continue to struggle, farms amalgamate and so on.
