If you can afford and have time, take the Helicopter ride (the one WITHOUT DOORS) and get the lunch at the "private waterfall".
Sounds cheesy, but without the door you have unobstructed view of the mountains on the Na Pali coast line, the fields where the dinosaurs ran in Jurassic Park, and loads of other great scenery.
The area with the waterfall is fantastic. (In fact, I would guess any tour that has a lunch stop will most likely be at a "private waterfall", and is well worth taking advantage of).
I have a photo somewhere of me hanging halfway out of the doorway with my camera, like someone out of a scene in Apocalypse Now. (pilot was not happy :-) )
It was more than we wanted to spend at the time, but WELL worth it in the end.
(Although I should add, if you're with a group of more than two, you may be forced into the back... and the view is not so nice. Almost certainly better than the helicopters with doors, but not as good as the front passenger seat. )
I would skip going out to the Jurassic Park set. The old entry way is a just a stick from the fence. Not worth seeing.
Although I believe that old strange-root tree is out there somewhere. (
Visit Jurassic tree at Allerton Garden - Honolulu Hawaiian Islands Travel | Examiner.com)
The waterfall landing pad is viewable from probably any helicopter ride, but not truly impressive out of context.
Other than the helicopter tour, I don't think there is a place on Kauai that you won't find worth photographing.
Obviously a wide angle; 16mm or wider. I think the 17-50 would be adequate. If you have something wider, take it.
I think the selection you have planned covers the range you'll want. But keep in mind, if you're going to do any walking, thats a lot of weight.
I would keep it simple with one or two zooms.
We didn't get a chance to drive or walk the northern area of the island.
We did snorkel off Poipu beach. Great photography opportunity. Much better than any scuba dive we have done.
Digital cameras and simple/affordable waterproof gear were not really available when I went. I would bring a waterproof bag for the DSRL if I got the chance to go again.