Powerscourt is DEFINITELY worth the visit (been several times) and allow an hour or two to walk through the gardens. The Powerscourt Hotel & Resort (formally Ritz Carlton Powerscourt), just "next" to the Powerscourt Estate & Gardens, is a lovely stop for high tea or lunch. I took my mother and aunt there when they visited me when I was living in Ireland for a year.
I've spent time in Waterford and Kilkenny. I found Waterford, like other people I know that visited, was a bit underwhelming. Also, I think they stopped doing tours of the Waterford crystal factory too...I'm not 100% sure. I know it wasn't offered when I went and I THINK I remember the staff saying they don't offer it anymore. Really, there wasn't much to see. We were there for a day and had to make an effort to fill up our time there. Spend more time in Kilkenny.
Kinsale is one of my favorite places in Ireland to visit. Charming fishing village...great seafood! If you like seafood, try Fishy Fishy Cafe.