Hi and welcome to an unbiased source of information.

If you have read any of my recommendations for similar ventures on other forums then you may note that I always recommend heading straight to Belfast from the Airport which is an hour north of Dublin to start with and head counter clockwise putting Dublin to the end. 15 days is at the minimum end of the time scale for the whole island and means quite a few one night stays or cutting out quite a few lumps.

To answer the question as is however...
No problems at all staying in Kilkenny for one night before moving on. I would only spend one night in Kinsale, it is a pleasant enough town and has clung to a small amount of the charm it had some years back. Use the night you save for Kenmare or to split the long haul from Dingle to Galway somewhere in Clare.  There are a few options from Galway as a base but if you spend the night in Clare you could aim for Clifden for the overnight and Conemara. Put 2 nights around Ballina or Sligo before crossing the border. I personally prefer Portrush to Derry. Then on to Belfast.

Thanks for your suggestion to add an extra night in Kenmare and areas in Northern Ireland.

I have thought about rerouting the trip and begin in Belfast, especially after reading a Fodor's trip report of a couple on a 17 day self-drive. Also, we don't arrive in Dublin until 2 pm so I had thought about going to Belfast and then counterclockwise. The problem was that all the guidebooks and web itineraries go clockwise - should take the road less travelled. I would just e-mail all the B&Bs already booked and change the dates. Dublin has already been booked so it will remain the same.

I wish I had found your forum earlier rather than relying on www.discoverireland.com referrals.  You are the only Ireland planner in the US with an on-line forum for free answers.  I contacted several as I was curious about what they did but none offered the information you do.

Thanks for your information about going counterclockwise in Ireland as allmost none of the many guidebooks and websites I read suggested this.  I regret that I didn't do a web search for Ireland travel when I started my trip planning.  For all future independent trips, I will definitely do a web search as well consult guidebooks & other websites.  Rick Steves did mention it and probably expected his readers to pick up on it as an alternative though his itinearary is clockwise.   We arrive in Dublin at 2 pm so this makes more sense.

I plan to rework my itinerary and contact the B&Bs to change my arrival dates, assuming they can accomodate me.  Contacting B&Bs by e-mail has a relatively quick turnaround.  I will definitely use your suggestions about the western part of Ireland, spend 1 night in Kinsale & 2 nights in Kenmare.

I have reworked my original itinerary, booked 2 B&B's and sending rebooking requests to those already booked.

Arrive 9/8, pick-up car and go to Newgrange, Hill of Tara, other Valley of Boyne sights;  Highfield House B&B in Trim

9/9    Belfast, Giant's Causeway, other castles and head up to Portrush; Anvershiel B&B

9/10 -9/11  Drive to Sligo or Ballina; Conmeara ?

9/12   Clifden -

9/13   Galway

9/14-9/15   Dingle - Dingle Peninsula, Slea Head

9/16-9/17   Kenmare - Beara Peninsula, Ring of Kerry, Muckross House

9/18     Kinsale

9/19     Kilkenny - Kilkenny Castle, Glendalough, Powerscourt (love gardens)

9/20-9/22  Dublin; early flight to US on 9/22

It seems that the drive from Portrush is quite long.  Should we  break it up with an overnight?