Do you think anyone besides an English Lit teacher would enjoy Bloomsday?

No experience here, but I just looked it up. Yikes. Your instincts are sound. I cannot imagine a group of teenagers enjoying this. Maybe if they'd done a unit on James Joyce, but even then. Can you offer to give her the afternoon off so she can go by herself?

They are reading Ulysses and teacher obviously loves James Joyce. They have 10 days and will try to do Dublin, Stratford, London, Paris. I'd like to skip Dublin even though it is cheaper to fly into.

Our Ireland co-author doesn't find Bloomsday of much general interest, more for people who do know the book, but it sounds like they will know something. Dublin has enough other sightseeing to make it worthwhile, if you have time in your 10-day plan.

Keep in mind the extra travel time or expense to get from Dublin to England by flying or by ferry and rail; see links mid-way down the page at http://www.ricksteves.com/travel-tips/transportation/trains/ireland-rail-passes. From London to Paris, book tickets on the Eurostar train 4-6 months ahead for best rates on selected departures.

Yes. If the students in the class are studying the book, and they want to go on a trip led by their teacher, then yes, it sounds like they are interested, doesn't it? To spend one day of ten, or a half day, observing and participating in the event sounds to me like an excellent cultural and learning experience for high school students. You seem to suggest that they would not enjoy it since they can't drink, I couldn't disagree more.
From the Wiki:
The day involves a range of cultural activities including Ulysses readings and dramatisations, pub crawls and other events, much of it hosted by the James Joyce Centre in North Great George's Street. Enthusiasts often dress in Edwardian costume to celebrate Bloomsday, and retrace Bloom's route around Dublin via landmarks such as Davy Byrne's pub. Hard-core devotees have even been known to hold marathon readings of the entire novel, some lasting up to 36 hours.
Wow, sounds awful! ;-))
Dublin is a wonderful city, with lots to see. Let them partake of some context for what they have been studying, take them to tour Kilmainham Gaol and the museums. See the great parks, take a day trip to Belfast and talk about the Troubles. This can easily be viewed by some as selfish on the part of the teacher, I would suggest to you that the teacher is passionate about their subject, and that's good for kids to experience.

I am glad she is passionate about the subject and if it is done well I like the idea of Bloomsday. I just wasn't sure if it was a literary festival or a really good excuse for a pub crawl. I'll let you know if it turns out well!

And I surely do understand your concern there. Perhaps doing the Ulysses thing in the first half of the day before the inevitable drinks really start flowing makes sense, and schedule something else-not the Temple Bar!-for the rest of the day.

"They have 10 days and will try to do Dublin, Stratford, London, Paris. I'd like to skip Dublin even though it is cheaper to fly into."

10 days, 4 stops? Ehhhhhhh......

Even if this doesn't include flight days, this is a lot. I'd cut Dublin, too.

Don't forget it will cost money - and time - to get from Dublin to London, so those savings may evaporate...

Is Paris definitely part of the plan? Its' a fabulous place, and would be a great experience for the kids, but with time and money factors, maybe everything's worth considering when deciding what to include and what to cut out?