It's an alternative, but is it even the best alternative?

The choice is not only between SNN and DUB. There is also (recently expanding) ORK (Cork), and given that it's further from DUB and "nearer to more" (Killarney, etc), I would propose that with a fresh look, it might be a better secondary Irish destination than SNN. SNN's choice as the secondary was simply due to it already being there (due to its history as the refueling stop back in the days when many planes couldn't fly nonstop Europe->US), forced onto airlines by people who wanted to find a use for SNN in the modern era. But with a free choice (with OpenSkies), I'm not sure why ORK
wouldn't be a better choice if AA ever wanted to fly to a secondary city in Ireland again (presumably only seasonally).

And it doesn't take that long to get to the SNN area (if that's where you really want to go, as opposed to further south/west) from DUB by train or car. But that's not even the direction you'd necessarily want to go (to get there efficiently) if your final destaintion is further south/west!