I haven't played Mauna Lani, but Mauna Kea is the best course I've ever played. Even though its not as private/exclusive as other courses I've played, to me it is the perfect combination of fun, challenging, and beauty. I'd definitely put it on my list if I were you.
If you'd also like to work in a (relatively) cheaper round while in that area of the island, the course at Waikoloa Village is a good option. Not as beautiful as others in the Kona area, but a chill, fun round on a course that goes through a neighborhood.