The population of Limerick city is roughly 60,000 right? That's about half the size of Swords....
I'm sorry, this assertion is wholly inaccurate. According to the 2011 census, the total urban population of greater Swords was 42,738. The population of the Limerick metropolitan area exceeds 100,000. For those who are not aware, the metropolitan figure is important as it includes the sprawling suburbs of the city that are outside the traditional city limits in counties Clare and Limerick.
While I completely agree that the catchment of SNN is indeed small and it certainly punches above its weight in some respects (and comfortably so), it is important to factor in neighbouring tourism and population centres of Galway, Ennis and beyond.
Personally speaking, the average tourist visiting Ireland in search of a bit of diddly-eye, Guinness and leprechauns would do well to avoid spending time in Dublin. Strolling through the city centre on a sunny Saturday this weekend, I was embarrassed to watch masses of tourists and gangs of spanish and italian students navigate the filthy streets and menacing crowds of Temple Bar while being continually harassed for money by junkies. It's just my view, but I really do think the average tourist (British stags and hens aside) would be far better off starting and finishing their journey at a provincial airport.