Two day stopover in Dublin. Worth it?

"worth it" depends on a lot of things, including your interests. Is it a full two days or two nights and one full day? Do you have to be at the airport for a very early departure? Are you ok with limited daylight hours (because it's going to be kind of dark then)? Is it over a weekend when things are busier? Are there things you want to see in Dublin? Do you want to spend money on hotel/logistics/activities in a place you're not jazzed about visiting? I don't think Dublin is "underwhelming" at all, in fact I loved it, but those kinds of questions would be deciding factors for me.

Is it a full two days or two nights and one full day? Do you have to be at the airport for a very early departure? Are you ok with limited daylight hours (because it's going to be kind of dark then)? Is it over a weekend when things are busier? Are there things you want to see in Dublin? Do you want to spend money on hotel/logistics/activities in a place you're not jazzed about visiting?

Interested in history, art, architecture, museums, and experiencing the general vibe of the city

Not interested in shopping, nightlife, bars and restaurants (on this trip at least)

Flight leaves Dublin around 4 pm

OK with it being dark

Will have from about 1 pm on day one until about 4 pm on Day 3. Wednesday through Friday

There’s nothing I particularly want to see in Dublin, because I don’t know much about it. Have heard of the Temple Bar and have no interest in that.

It was certainly worth it to us. I'm not a fan of cities, generally, but we thought we should at least experience Dublin before we left Ireland. We loved it. We didn't get to do that much in two days but had a great time and enjoyed everything we were able to do.

"worth it" depends on a lot of things...

Another major thing (the one which I'd argue is most important) is...

Compared to what alternative?

Is a two day stopover in Dublin better than two days in a hospital getting your appendix removed? Absolutely.

Better than sitting at home and dreaming of Europe for two days? Yeah, I'd say so.

Better than spending those same two days enjoying being in Italy? Well, now you're down to setting priorities and making trade-offs (which is what travel planning is all about).

Is your trip to Italy as long as you want it to be? Or have you cut corners, squeezed your itinerary (or skipped places entirely) to make your trip "fit" a too-short window? If you won't have had your fill of Italy when you reluctantly board your flight home...maybe those two days would be better spent in Tuscany or Venice, slowing your pace a bit and allowing you to savor things or add one more short stop at another location. How would you prioritize spending those two days? Only you can say if anything is "worth it" – because it's completely subjective. And it's always about how else you might use that time.

FWIW, I've never heard anyone say that Dublin was "underwhelming." If someone told me that, I might not take their recommendations very seriously, but that's me. (Hey, I fell in love with Latvia, so what do I know?).

There's plenty to fill a couple of days in Dublin. I recommend Kilmainham Gaol (reservations usually a must, although I don't know about mid-December), Christchurch Cathedral and St. Patrick's Cathedral, and the Long Room in the Trinity College Library (although most of the books aren't there right now due to conservation), which can be visited along with the Book of Kells (although I was far more impressed with the library than with the BoK). There's Dublin Castle, also, although we saw only the outside, so I can't comment on visiting the inside.

There are also some great day trips from Dublin, such as visiting the Boyne Valley and Newgrange or visiting Blarney Castle and the Rock of Cashel.

We spent a week in Ireland on our way home from Croatia. We visited both Belfast and Dublin in that week, and took a day trip from Belfast and two day trips from Dublin. We know we only scratched the surface of Ireland, but we loved what we saw and weren't underwhelmed at all.

IMHO the answer is yes. If you not been to Eire before than why not? When flying into Dublin Airport be sure to look out the window. On my 1st visit was flying over from London. As the clouds cleared and I got my first glimpse I uttered “ bad word, it really is that green!”

Upon seeing The Long Room at Trinity College my friend ( an avid reader ) announced her desire to be buried there. Last name is Collins so who knows?

The immigration museum is well done. See what’s on at the Gaiety Theatre. https://www.gaietytheatre.ie/

Personally I’d take a bus out to Powerscourt Estate.

Lastly, Newgrange is fascinating. Read up on it.

So my answer to your question is yes.

Will have from about 1 pm on day one until about 4 pm on Day 3.
Wednesday through Friday

So you have one late afternoon/evening, one full day, and most of a morning before you need leave for the airport? That is enough to get a flavor of Dublin proper. I personally loved the National Museum (cool bog mummies), the National Gallery (art), Book of Kells, a musical pub crawl, and just walking around the central part of the city. Do not rule out bars/pubs - it is THE vibe of Ireland. Given proximity to the holiday season you may have some seasonal activities to choose from. I regret not going to Newgrange, but if you do that it will eat up most of your full day, as will any other day trip already suggested. I'd stay in Dublin.

If you are US citizen allow yourself a generous amount of time for your departure as you will go through US immigration process in Ireland.

Although I love Ireland, I am not a big fan of Dublin.it certainly won’t give you a good feel for Ireland, which IMO is all about the small towns and gorgeous green countryside. However, Dublin has some great sites, which are worth seeing, particularly Trinity Library and the Book of Kells. If you have the time, I would do it.

I would agree that Dublin is underwhelming and also dirty. I wasn't interested in shopping or bar hopping either.
We were there for almost 2 days also. The 1st day we saw 2 parks , St Stephen's Green and Merrion Square Park. The next day we went to the National Museum of Ireland and the Chester Beatty Museum as well as the exterior gardens of Dublin Castle. Those 2 museums are worth seeing.
We then went to Trinity College to see the Book of Kells but the tickets were sold out and we couldn't come back. After the fact, I heard that you can only see 2 pages of the book.

Just because you're flying into DUB doesn't mean you have to stay in Dublin.
You could go to Belfast instead. Direct bus from DUB airport or go into the city and take the train. The black cab tours offer a look at recent history from people who lived/are living it.
You could rent a car and go see the Giant's Causeway or the Cliffs of Moher (along with lots of beautiful green countryside along the way). I personally would not do this, as I don't like driving over there in the summer, let alone the short, gray days of December.
You could take the train to Cork, with a day trip to Cobh or Kinsale.
Or Limerick and get Paddywagon to take you out to the CoM or the Ring of Kerry.

I found the hotels inexplicably more expensive in Dublin which given my own tastes when it comes to tourism makes it not worth it after coming from Italy.
We have two flights a day from Chicago to Dublin on Aer Lingus and that airline has some of the lowest fares to major cities in Europe connecting through Dublin.

Add me to the list of people who found Dublin underwhelming. I didn't find it any dirtier than any other European city.
I enjoyed my trips to Howth, Dalkey & Killiney far more than I enjoyed the city. I'd love to return to Ireland and bypass Dublin entirely.
But if you've never been to Ireland before, sure, why not? I wouldn't pay a whole lot extra to do it, though.