You may have a point about the yearning being a by-product of the unwilling emmigration. It makes me cry to think of it. In fact, for some of us, it may not be healthy to think of it too much; so many broken hearts.
Even before the famine, there was significant emmigration due mostly to population density and poor prospects. The people who worked the land did not own it, and the lure of open country was powerful. Families were broken and so the hearts followed.
For a once in a lifetime visit, where would you not want to see? I could not tell you! I'm a big fan of the wild west coast myself, but there are so many distinct areas that have their own charms. At this point, though, I would avoid the main roads and the cities. From what I gather, the new fast roads are not the way to see the country. It really depends on what you like to do. Some people could make an entire holiday of chasing down holy wells (I could.) Others would like a spa holiday where they could go be pampered. Some people want to get as many "places" under their belts as they can. Then there's the whole of Northern Ireland, which is absolutely gorgeous.