Arklow, Gorey and Enniscorthy are also reachable from Dublin by rail within a couple of hours and have nice beaches nearby. However house prices in the first two towns have risen sharply over the last few years as they have additional commuter trains to Dublin, as well as the Rosslare services. Unfortunately the future of the line beyond Gorey to Wexford and Rosslare is still in some doubt, despite it having been relaid with CWR and resignalled within the last 10-15 years. A lot will depend on Irish politics and budget priorities. The biggest scandal is that Rosslare Europort, the largest and busiest port in the Republic, has no rail freight facilities whatsoever. Everything going on and off the ferries goes by road. if the government can be persuaded to change that situation - and also reopen the Rosslare-Waterford line - then the future of the Gorey-Rosslare section will be assured, although a lot of track doubling and/or additional passing loops will be required.
Many British people have holiday and/or retirement homes in West Cork and Kerry, including friends of ours. The scenery, ambience and beaches are very like Cornwall, as is the climate and weather (both good in Summer and bad in Winter). However, public transport-wise, you would face a long bus journey to/from the railheads at Cork, Killarney or Tralee, connecting with an even longer train journey to/from Dublin. There are airports at Cork and Farranfore (between Killarney and Tralee) with direct flights to the UK.
I sympathise with your desire to obtain Irish citizenship and therefore the entitlement to an EU passport, but I think at that, at the moment, this is only available to people with at least an Irish grandparent. Good luck!