Good players want to play with and against other good players. Being the tallest midget in a poor conference won't get ND any closer to the CWS. ND baseball, especially in its current state, will undoubtedly take its lumps as a new member of the ACC, but over time I believe playing in the ACC will be a net positive for recruiting. Look at the basketball program. It was a whipping boy upon joining the Big East, but being a member of the strongest basketball conference in the nation forced the program to improve and has helped recruiting.
I have plenty of other reservations about joining the ACC, but baseball isn't one of them.