Problem is Dublin is nowhere near 20 million passengers and will not be for a considerable time.
The era of cheap flights and weekends away is over, the Irish economy still has a lot of bloodletting to do in the Public sector and on welfare recipients so this will reduce spend available over next 5 years.
My comment regarding Tax I think you misunderstood as the €50 is what will be the Govts / EU take not the airlines price.