Is it worth getting both of these passes if we are traveling from Dublin-Kilkenny-Ring of Kerry-Cliffs of Moher-Galway-back to Dublin?
Do your research compare the prices. I didn't find that the Dublin Pass was that great of a deal. You didn't mention how many are in your party -- we got a better deal with family rates on attractions and buses. For the buses in Dublin, you can get an individual day pass for 6 euro or a family pass for 10.
Jan, my wife and I circled Ireland on a trip similar to yours in May. The Dublin card works only if you intend to be REAL busy during your Dublin visit. You can walk almost everywhere so you're probably better off only buying transport tickets as you need them. On the other hand, for your itinerary, the Heritage Card is a GREAT deal. You'll need one/person and you can buy them at the airport when you arrive or at your first visit (ie Kilkenny Castle). Also at the Kilkenny TI, ask about the Ireland Heritage Pass (good also in N. Ireland) - you'll only need one/party. Google the details of each.