I agree with much of what has been posted here, particularly the observations of Allen, Paul W., Mr. Barker and my old bud Huck.
I've been on two golf trips to Ireland for 15 days in '93 and 20 days in '97. On both occasions we played in every quadrant and did not find the playing/traveling dichotomy overly taxing.
Trip one: Royal Dublin, Portmarnock (36), Mt. Juliet, Tralee, Ballybunion, Waterville, Killeen, Lahinch, Connemara, Sligo, Portstewart, Portrush then County Down.
Trip two: Portrush, Portstewart, Sligo, Enniscrone, Carne, Connemara, Lahinch, Ballybunion (Old & New), Tralee, Waterville, Killeen, Portmarnock Links, Portmarnock, K-Club, St. Margarets, Baltray and County Down.
I've met a number of guys who have gone on 8 day golf binges there and claim to have had a thoroughly good time playing 36 holes a day. That may be true for them (although I tend to chalk that up to testosterone hype) but this I know about me; I wouldn't for three reasons.
First, I want to enjoy the course and take it in, remember and savor it like a fine bottle of wine. Playing the same course for 36 might work in this respect! Playing two different courses in the same day leads to confusion in the old memory bank for me.
Secondly, we're not talking Myrtle Beach or Southern California here, riding carts in perfect weather! It will be windy almost certainly and the weather can get downright nasty, for the day or parts of it. Your rainsuit and umbrella will probably work overtime. You will be physically taxed playing and walking in those conditions. Playing 36 hole days will guarantee to exhaust you and you WILL NOT be playing anywhere near to your usual form as a direct result. Also recognize that these are difficult courses and you will be taxed in playing them to your capability anyway. So it's a choice, rip off these gems and notch your belt, or take your time and play them with the care and attention they merit.
Third, even Huck recognizes that there is something inherently fun about playing a game o a great course then repairing to the pub for Guiness and pub grub and bantering with the locals. The people are almost as much fun as the golf! Those opprtunities are surely missed if all you do is golf, golf, drive, sleep, golf, drive, golf, drive, sleep, etc. It's only my opinion, but I swear to it, enjoy the WHOLE experience.