A couple of observations I can offer, as my wife and I were in that area last week -- I didn't find Galway very interesting at all. There is a very heavy college student presence in the central city area and the old part of town is really not that interesting from an architectural or historical perspective (speaking as a non-architect). I have to warn you, though, that I live in a small town in France that has structures ranging from the early Middle age to the Renaissance, and I've traveled extensively in France seeing sites from pre-Roman on through to the modern era, so I may be a bit more "numb" to that kind of stuff than some folks whose idea of an old structure is the county courthouse built in 1876.
As a city, I found Dublin far more interesting and, for small towns, places like Kinsale, Kilkenny, and Dingle also were more interesting (to my wife and me) than Galway. So -- I'm not sure Galway is even worth a stop if doing so would impede your other activities.
We planned and did drive the Ring of Kerry, the Dingle Loop (aka Slea Head), and we visited the Cliffs of Moher on the way to Galway. Although last week was generally great weather in Ireland (unusual, we were assured by practically any Irish person we spoke with), the day we allocated for the Ring of Kerry was complete with rain, drizzle, fog, and very low clouds, though parts reminded me of the hillsides and valleys near our house in southern Bourgogne, if one substituted black-face sheep for Charolais cattle. But we saw little of what many folks rave about at the Ring of Kerry. The Cliffs of Moher and the Dingle Peninsula, however, had clearer weather, so we could see and experience far more. So -- my point is that you should retain flexibility given the unpredictability of the weather. If one is fogged or clouded in on the day you're there, perhaps you'll have better luck on a later day with another. As for the length of time at Cliffs of Moher: unless you plan to hike or walk along the path extensively, you could probably get by with 90 minutes to two hours there.
As an aside, the visitor center at Cliffs of Moher was underwhelming, though some might be fun for kids. The Blasket Island Visitor Center on the Dingle Peninsula, by contrast, was extremely well done and worth an hour or two. As an American who has long been immersed in the story of European immigration to the U.S., it was very interesting and sobering to read about the effect that migration had on the emigrant communities whose young people left for the new world.
