I just wrote a long response to your question and it disappeared when I was copying it in case it disappeared. Frustrating.
Anyway, this will be shorter: On my trip I remember at least five other solos: four women and one man, a couple of them in their 40s and still working. We seemed to have different interests and all kept busy on our free time. I'm interested in history and museums and spent a lot of time in the Archeological Museum in Dublin (photos allowed) and in art galleries and at historic sites. I took an excursion to Newgrange, which was wonderful -- no photos inside the passage tomb but the outside is interesting too with the huge carved stones. The Hill of Tara was included on the tour but it was raining too hard to climb to the top, but we got partway up. If interested, you need to book the tour on your own on the internet before your trip.
I needed to ask directions several times and always got cheerful, helpful answers.
Ireland is very pretty and photogenic, and abundance of opportunities for great photos. I took breakaway travel in Dublin and stayed in the same hotel, which is fairly well located. I had a list of what I wanted to do and see there was little time alloted on the trip. I could have taken one day. So I recommend doing some research and deciding if you would want to stay on.
Re safety: I'd rely on the advice of the PD. On our city tour she recommended staying away from one section of Dublin at night. I think you can find information on the web too.
I think you'd have a good time and needn't worry about acitivity level or someone to hang out with. You will be experiencing the trip with others during excursions, breakfasts and other included meals, it's just that you may not find someone with like interests during the free time.