vkid - I don't mean the small sums you quote there (assume they're correct). I'm thinking more of the new/refurbed terminal that was done 7/8 years ago (not sure on that timing?). Major pieces of infrastructure like that are the level playing field I'm referring to.
Agree with 840 on the regionals. I think they should have enough facilities for basic services to Dublin (which should die when/if we get motorway and/or fast rail from each urban centre - i.e never for Mayo, Donegal and Kerry), London and a small number of other half decent routes. Ireland is too small for each airport to have it's own full suite of routes to every destination under the sun. Sligo is a perfect example, they have Knock to the South, and Derry and Carrickfin to the North. There should be no further investment there for instance. (Wait for the barrage of comments from Sligo people...)
I would make the case for Carrickfin, as the north of Donegal is as remote as you get on this island of ours. It takes a long time to get there to anywhere! Caveat again, it should just be a basic route to Dublin and/or London, nothing more.