I fly alot stateside with Aer Lingus. I think the business class is expensive for the service you get. Seats or good though, especially the newer planes. Overall the business class experience is like the economy experience: ok but far from luxurious.
Due to frequent flyer status I get lounge access for all flights with AerLingus, which is nice, but not life changing.
Usually only go business coming back from US, but not going there - or if it is LA flight (11 hours is very long in economy, especially with AerLingus)
(Flying mostly to Seattle and DC)
If the price difference one-way is less than 1500 euro at time of booking I might consider it for a return flight depending what my plans are for the day of arrival.
I usually ask at check in, and if they offer an upgrade for around $800 max I tend to take it.
It is a far cry from the business experience with the Emirates or Etihad. Delta premium economy had better service than AerLingus business (seats are not comparable)