Iceland Air offers good connections into northern Europe. I would try to fly them and layover in Iceland. I enjoyed Iceland more than the UK.
Europe has a lot of half or full day tours of major cities. You end up seeing old buildings and traffic. Ok for orientation if you want to come back on foot later, but not my thing. Or you could rent a car, do picnics, stay in small or B&B type places., and meet some locals.
If you did not do Iceland Air, I could consider flying into Shannon rather than Dublin and focusing on the less populated west coast of Ireland. Then ferry across to do a distillery tour of Scotland.