Mark, I doing Dundrum as my last hard-paced piece of work before Dublin - though I'm a marathon first-timer so my advice perhaps not so valid. I've followed the Pzitzinger & Douglas 18-week schedule and after Dundrum I will rest Sun & Mon, 6m recovery pace Tues, marathon pace 8m Weds, Rest Thurs, 5m Recovery & Strides Fri, 4m Recovery Sat & rest Sunday.
I ran Dundrum last year & now I have other races to compare it with, I would definitely recommend. The boardwalk & beach sections break up the road/track sections although, last year, the strong headwind made the 2m beach section really tough - but it's only 2 miles! The tide was well out (haven't checked the tide tables but assume it will be well out again!) and we ran close to the dunes on reasonably hard sand - my Garmin records show I was almost 1min/mile slower on the beach section.
You've reminded me to enter - hope weather is kind to us!