Is Dublin worth a visit or go in and out of Shannon and stick to the southwest area?
How long is your trip? Do you already have airline tickets? Do you want to see a city or do you prefer small towns and countryside?
More details will give a useful answer. Dublin certainly has several days of sights, but may not be what you want out of this trip.
I loved Dublin to to me, it is for sure worth a stop but like Harold said, how much time total do you have ? How are you getting around? What are your interests?