I've been at a wedding in Brook Lodge, it was very good, but I think the place has got very trendy and can imagine that if there was a function on the place wouldn't be too peaceful.
My absolute favourite is the 5 star Heritage Hotel at Killenard, Co Laois (not to be confused with its sister hotel, the Heritage in Portlaoise).
The website is [broken link removed] and if you click on breaks you can see the special offers.
The hotel is gorgeous, you can eat in the upmarket Arlington restaurant (I haven't tried it) or in the Slieve Bloom bar (which I think is better for lunch). The spa & leisure centre is in a building next door to the hotel, and the golf clubhouse next to that. You can also eat in the clubhouse bar or restaurant, very good food (I've eaten there a few times). Also there's a little coffee shop on the ground floor of the clubhouse building.
Also there is an Italian restaurant on site which is very reasonable and food very good, and a pub adjoining which does a carvery lunch.
I'm vegetarian and have found myself very well looked after at the Heritage, was there last June and over the recent Paddy's weekend.
I've done the "Spa Experience" three times now and love it. For 60 euro you can spend 3 hours doing hot & cold. You go into 1 of 5 hot rooms to warm up, then you have a cold (or cool) shower to cool down again. There's an area with footbaths, and a hydrotherapy pool with massage fountain, and a juice bar to keep hydrated. At the end of it you feel so relaxed and laid back. I thought the prices here were reasonable enough compared to what I've seen in some places.
If it's Wicklow you want, Powerscourt Springs might be an option? I haven't stayed there, but have heard great things about it.