My parents are owners at Kona Coast II, so I've stayed there several times. It is a very nice resort, but some of the units are starting to show their age. The last time we stayed there, in Dec. of 2002, our unit had multiple problems (no blinds in the kitchen window, ceiling fan didn't work, other glitches I can't remember) and we had to move to another unit after just one night. So if you do stay there, be sure to inspect your unit when you arrive and let the front desk know if there are any problems.
And re the "beach" -- most of the beaches on the Big Island are pretty rocky, and the one at KCII is no exception. For a sandy beach you have to go north to the Kohala Coast area -- there is a very nice, sandy, public beach several miles north of the major resorts up there (sorry I can't remember the name). It would be a 45 minute drive from KCII. If you want beaches, then Paniolo Greens would be closer, but it would also be farther away from the shopping, fishing and restaurants at Kailua-Kona. The two would be about equal driving time from the Volcano National Park.