Compare the benefits another way:
Over the life of both stadia, consider [cost of land aquisition] + [cost of development] - [direct return (tickets, catering, pourage etc.)] - [indirect return (restaurants, bars etc.)]
It's not going to be as simple as "we get more direct and indirect return" if we also have more expensive aquisition and development. I'd bet a fiddy that it costs less to do construction at Penrith than Moore Park, and that on top of the cheaper land costs in the beginning means that you might wind up with a more viable stadium over the long term at the 'ruff than the SFS.
Tricksy little factors apply as well - people *can* drive to outer suburban stadiums, and really can't to city grounds. If crowds are smaller, the ground can be smaller -> less maintenance cost. Noise and traffic issues might be less, so you might get away with more events, and more events = more paydays.
It depends on whether its part of a strategy to increase the size and growth of the CBD rather than continuing urban sprawl. Crowd attendance inadvertently increases due to the other facilities around the stadium, the denser population.
We are talking about inner city Townsville on (Government land?), using some of the unusued railway land.
I am far from being a capital city only stadium fan (eg my support of Thomsons Lake as the best site for a stadium in Perth, particularly due to the costs of Perth CBD sites and the fact you had a greenfields site with all the infrastructure benefits of an inner city venue. ).
But I can see why its in the Government's interest in Queensland.