I would agree with myrrh, and I think that (depending on the rest of your background, obviously) if you do well in either program that you would have a good shot at UCD's ARE PhD program. For what it's worth, of the 19 incoming students this upcoming year, 2 appear to have carried on from the UCD ARE MS program (not sure how many from the program would have applied to continue on though).
I will PM you with some other thoughts shortly.