I have been to both Ireland and Barcelona. Two totally different places. If you are committed to November, I would really consider the weather issue. We were in Barcelona in late October and it was cool but the weather was sunny and just perfect.
We were in Ireland in February and had two days of sun but five days of rain and mist and 40's/50's temps. Summer is a much better time to be walking in Ireland. Check the weather information on weather.com and you can see the typical patterns of both temperatures and rainfall for each place.
Good luck making your decision. By the way, I loved both places. As a city, Barcelona is so vibrant with so many things to do. I haven't been to Dublin but that's on our list.