Kona is my favorite tourist town out of all tourist towns I've ever been to. Nice, clean, small enough to walk Ali'i drive in one go.
My wife and I fell in love with the breakfast at Bubba Gump's - not Hawaii specific, but fun. Lunch and dinner are average.
There is an awesome cafe south of Kona called the Aloha Angel. It's on the right side of the highway in Kainaliu just south of Keauhou. Go for breakfast, and only if seating is available on the lanai (I read a review or two that said the lanai was closed, which would be weird). Food was great, service friendly, and the kids loved feeding papaya to the geckos...
The last time we were in Kona we gritted our teeth and did the timeshare presentation to get helicopter rides cheap. Not fun, but the 1.5 hour investment was worth it in the helicopter ride (which took off from the airport in Hilo). The volcano was cooperating that day and we got to see flowing lava, fly all the way around the Pu'u O'o vent, saw the lava flowing into the ocean. We flew with Blue Hawaiian and the pilot was great - fun, nice, informative, but also knew when to be quiet and let us appreciate what we were seeing.
If you want to laze the day away on the beach it would be hard to beat Hapuna in the Kohala district. Spectacular white sand beach looking out toward Maui.
There's a cool botanical garden on the windward side, north of Hilo - can't remember what it's called, but when we checked in they gave us a huge bunch of apple bananas and some juice to enjoy while we wandered the garden.
Kahalu'u Beach Park just south of Kona is our preferred place for snorkeling. I'm sure there's better snorkeling on the island, but my wife is very nervous around the water and Kahalu'u has a very old breakwater that keeps things calm (I've heard it was built by King Kamehameha, but I'm not sure of that). We've seen lots of fish there and had some great face-to-face encounters with sea turtles. It's the only place locals ever gave me shakas :shaka:. A guy weaving palm baskets liked my Bugs Bunny tattoo.
I think I need to go back...
On my list for next time we go is getting in touch with Chuck Moore to see if he'll show us his operation...