We stayed at The Westin about 6 years ago. It was really nice. We had an ocean facing room, the sunsets were awesome! It faces the smaller island of Lanai. The pool is a bit of a nuthouse, but the big water slide is fun. The beach down to the right, you can see it of in the distance in the photo of me on our deck, was really great, the one in front of the hotel is a bit narrow. Kaanapali is central, but if you want to go to Paia for lunch, it's going to take at least 45 minutes. The sushi/fish at the restaurant Sansei is amazing. http://www.sanseihawaii.com/
The cute town of Lahaina, 10 minutes from The Westin, is full of really good restaurants. The beaches/resorts south of you in Makena, are worth visiting. Big Beach is awesome for nice waves. Make sure you drive to the top of Haleakala Crater, it takes about 90 minutes, and bring a sweater. Maui is very different than Kauai, it has endless white beaches, parts are really over-developed, but it is so easy to get around and has a wonderful, bohemian vibe around the town of Paia, we stayed there for 1/2 the trip. I didn't get to Hana, a really long drive, but it's supposedly very cool in the end of the world
kind of way. Have fun!
Here's some pics: Room at Westin:
View of Lanai from balcony:
Westin balcony, nice, wide beach off in distance:
View inside the Haleakala Crater: