That said, I second visiting the Big Island and visit various sites. Driving less than an hour and going from barren volcanic landscapes to lush rainforests was something else, and watching the sunset from Mauna Kea was magical. And lots of great beaches, and most that weren't next to a resort had very few people.
While the island is big relative to the other Hawaiian islands, its small enough that you can drive around it in a day.
I'd recommend staying on the Kona side, which is the dry and somewhat barren side. The Hilo side has rainforests for a reason.