to Debi-absolutely spring for the heli tour on Kauai! I did it 2 years ago (by myself, as the ex was not interested) and plan to do it again this summer when I take my boyfriend for his first time. I can't come up with enough adjectives to describe the feeling you will get and the scenery you just can't see unless you do the heli tour. I took some amazing pics and Blue Hawaiian Helicopters did a dvd of my ride, so whenever my memory gets fuzzy, I can feel it all over again in vivid detail.....
I can also vouch for the safety of Blue Hawaiian Helicopters, we had a safety switch that malfuntioned when they did the pre-flight check, and although the problem was just the switch, and nothing mechanical, they put us on a later flight just to be safe. Although it wasn't great having to wait a couple hours, at least we knew they don't take chances. It gave me a chance to shop, and I found a fabulous aloha dress in the small mall complex that their office was in. Also, they gave everyone in my group the dvd for free because of the inconvenience (since we were already at the heli pad waiting to board when the problem was discovered).
As far as Waipio Valley, I was along for the ride when my ex decided that our rental Jeep would be just fine going down the steep road (and a couple local surfers caught a ride down with us as well). I was freaking out, but luckily nothing bad happened, except we almost got stuck in the deep, soft sand from the beach at the bottom of the road when we were going back up. It was scary but beautiful, the black sand beach, with the waterfall to the left, is where Kevin Costner's character lands in the end of the movie "Waterworld". Plus a young couple came up to me with a camera and asked me to take a picture of her and her new fiance-he had just proposed to her in the Valley a few minutes before.
If (when) I ever get back to Big I, I want to do the horseback tour into the back of the valley...something the ex wanted to skip in favor of fishing (and we didn't even see a fish, much less catch one). If you decide to try it, 4 lo and verrry slow. Be aware on the way back up that those coming down have the right of way....and there is a blind turn coming down that I suggest you honk your horn because we would have had a truck on top of our hood, had the local coming down not honked there!
good luck!