I agree with the day trip to Hilo. We have done the Big Island a few times and I always stay on the Kona side towards Waimea-the area gives me fond memories of trips to Arco, ID.

Two Step beach is the best snorkeling in Hawaii but get there early, the Temple and the drive to Volcano NP is pretty much the same as from the Hilo side.

You are also closer to the Waimea Creamery. It. Is. That. Good.