Hi Keith,
Although I didn't get a stamp from the local parish church, I did get a stamp, and an Irish Pilgrim's Passport, from St James's Church beside St James's Gate in Dublin the day before I left Dublin. St James's Gate is now most famous as being the home of the Guinness Brewery (where one can also get a stamp!) but was previously known as the departure point for Irish pilgrims setting out for Santiago. Although this church was only built in 1840, it seemed like a symbolic link to the pilgrims of yore, as there had been a shrine close to the spot for many centuries.
I'm very glad I did that, and will do something similar the next time.
If it feels good to you to do it, do it. However, most peregrinos only pick up their credencials in StJPP or Roncesvalles and get their first sello there.
Buen camino, whatever you chose to do.
Maria