I am trying to decide what to pack for my two week Ireland trip. Is the theater dressy in the evening? I would rather not carry around a pair of heels for one night if I don't have to.
Since nobody else has replied: there's no need to make a special effort in dressing nowadays for London theatres (unless it's the Rocky Horror Show) and I'd be very surprised if Dublin (I assume) were any different. But it might be worth looking for more Ireland-specific forums.
I have attended both the Abbey and Gate theaters on several occasion and dress ranges from blue jeans on up to suits and what I would call evening dresses but as a whole dress is casual. I would leave the heels at home. How many of the people in the audience will you ever see again?