On the whole, The Republic of Ireland does not give a shit about a "United Ireland" anymore. There's a myriad of other issues that a lot more topical really, and I can't imagine that this one is ever going to come back to the forefront of public thinking ever again.
And far too much time has elapsed for the cultural differences between the two to ever be reassimilated. It would never work.
A - 2016-2022 will have a series of 100 year anniversaries, in the past anniversaries have seen spurts in Republicanism
B - Most Irish people in a recent poll still identify as Republican
C - East and West Germany were also thought to be too different, same with the 2 Korea's, however why should they not also reunify. As I said Dublin and Cork don't have the same culture so why should Dublin and Belfast.
Its typical for people from the far South to dismiss Irish unity, because well it doesn't suit them but in border counties notably Louth and Donegal its still some what present.
The fact Irish people will actually roll over on this issue is a representation of how they roll over on anything and are the most passive and apathetic people in Europe if not possibly the world.
The other issues that you mention Irish people clearly don't care about either or they'd engage in actual social mobilisation such as mass protests.
People here are so lazy