All ancillary revenue is vital for airports.
I fear that's a case of not seeing the woods for the trees.
If the extra passengers it generates can make a route or frequency viable, the lost parking revenue will easily be earned back through other fees earned by the airport, whether landing fees, pax fees or parking fees being paid by passengers who wouldn't be using the airport if the route/frequency didn't exist. It would also mean capturing passengers who wouldn't use the airport at all otherwise.
I'm also unconvinced by the need to be near a main road. If extending through to Cork Airport works for Citylink (who are trying to run at a profit), it could just as easily work for a number of Bus Eireann services.