For the South West the must sees are Ballybunion, Waterville, Tralee, Lahinch, Doonbeg, Old Head -the golf course is ok but the views are something else.
For some gems off the beaten track Dooks has just finished a remodeling by Martin Hawtree this summer, haven't played it yet, but heard good reports. Ceann Sibeal is worth a look as well.
There is a new course open at Waterville called Skellig Bay ,also worth a look.
If your base is Killarney, the courses there are worth a look as well, Killeen has just finished a remodelling as well, again haven't played since it reopened, but have heard good reports as well. Mahoney's Point is a nice course, not too taxing but good views of the lake, unusually large greens can put a bit of pressure on the putting (or approach play)
I live up the road from the Old Head and am a member at Cork GC, I think it fits your description ideally, off the beaten track of the southwest and would blow their minds. It's in an old quarry running along the Lee estuary. MacKenzie came along in the 20's and put his fingerprint on the course, a lot of variety and some really memorable holes, especially in the quarry stretch, plays really firm and fast in the summer as well.
Fota Island is just down the road from us, slightly more modern but worth a look as well.
If you tell when you are planning to come, I might be around.