Lots of arguments missing the point of Dundee Airport.
If you want to travel for £5 you can get a poxy bus all the way to Prestwick and travel on Pikeyair, having taken hours to get there. You could get a luxury coach to Edinburgh, taking you an hour or so, then spend another hour (minimum) getting through the airport and onto the plane. That would save you a few quid as well. Take half a day mind you but you'd maybe save the price of a tankful of petrol or so at the end of the day.
Or you can take half an hour to get from your car to the plane at Dundee and be in London before your luxury coach or poxy Prestwick Megabus even pulls into the airport.
There may be better ways to spend public money but as lots of it seems to get pissed away by incompetent public officials I would say it will be well spent on Dundee. And that's before you even start to consider the fact that it will become a significant tourist destination in its own right when the V&A opens.