Thanks everyone for all your suggestions. Here's what happened.

My flight arrived at DUB a bit early. The weather looked nice, so I decided to venture into town. I bought a €12 roundtrip ticket for Aircoach, and didn't have to wait long before hopping on a bus. 20 minutes later I got off at the Grafton St stop, the traffic wasn't bad at all. I went to Bewley's for breakfast. Afterwards I walked around for 90 min or so before hopping on the bus at the Suffolk St stop for the 25 min return trip back to the airport.

Everything went smoothly, and it was definitely a pleasant layover!!