I was there in the summer, and it wasn't at all what I expected...humidity wise. You'll discover the north side of the islands are more tropical, and the southern sides are more arid.

Kauai has some extraordinary scenery. The Jurassic Park waterfall scene was filmed there. I've flown around the island, and it's beautiful. Haven't been around Maui, but I've heard it's pretty amazing too.

It's expensive, and you need to remember there are three price "tiers."
(1) The locals price, which is the least expensive.
(2) The haole price, which is more than the locals price, and
(3) The tourist price is the highest. You'll be paying the tourist price.

If you are on the east coast, consider vacationing in Aruba instead. But there are other great Caribbean destinations too.

I considered visiting Hawaii as "getting the check in the box." It just isn't worth the expense to go back IMHO.

Enjoy your anniversary!