IMO, a character that was credited as guest star should have a page, no matter how minor his role was
I agree with this. However, the guidelines are a good way to decide if a costar (or even character that never appeared *cough*Briar Rose*cough*) should get a page or not. I would include one other guideline: The character is based on a character from literature, film, etc. In my opinion, part of the point of Once is they adapt things from various sources, and that should be taken into acount when we create pages.