I have walked to Croke Park more times than I can remember to hurling games.
So I would definitely recommend walking as it isn't too far from the city centre, as the others have said.
Jurys Croke Park will get booked up very early for the gig, so I think the suggestion of Jurys Parnell Street is a good one.
If you are doing a lot of shopping it is even near enough to many of the shops to bring some stuff back and have a rest before going off again.
I would suggest booking it now though, because I would think that a lot of the concert goers will have the same idea.
They have a good room rate all year round.