This topic seems to come up on this site every year about now.
The problem is that there seems to be no perfect "fire bomber".
Each fire is different and the final cost of each fire is different.
The final cost of a fire may or may not justify the large cost of a large or very large aircraft kept on standby for a season in an area.
I was at the site of the NSW Springwood fire a few years ago. My parent lived in the adjacent retirement village and I was taking them home when it started in a nearby paddock. When I first saw it, it was a small grass fire.
The cost of that fire was huge and despite denials, people died as a result. The problem was that they were old and died as a result of being moved off site into sub standard accommodation. Was the cost of their deaths factored in to the cost? Not that I saw.
The problem of that fire was that early on the resulting traffic jam stopped ground based fire vehicles arriving and the fire got away. Early this year I watched the DC10 drop retardant on a fire north of Wollongong. I have no doubt after watching that drop that the Springwood fire would have been out within minutes if the DC10 had been available. So I have no hesitation in saying in the Springwood fire the DC10 was the perfect aircraft for THAT fire.
As far as the criticism of old airframes, the CV580s, C13os and L188s seem to be working well elsewhere. The newer Bae 146 etc still have to prove themselves. The fact is that low utilisation vehicles and aircraft cost wise will always be leftovers. The economics aren't there for new equipment. The trick here is to pick good solid, reliable aircraft and the CV580 is just that.
Wunwing