ncmbm will tell you anything but a Hobie 14/16/17/18 is a fragile boat. I've owned all of those and raced the "Miracle" for a few years.
The first one I bought was a '94 and had some deck, soft spots aft of the front beam and around the board trunks. I sold it and bought a '93. It had hairline cracks on the hulls inside of the front beam and on the transom at the deck joint. I was told (by more than one 20 racer) these were both problem spots and should repair both. I repaired neither and in two years of racing they never got any worse.
The boat is prone to denting, but aren't most later designs? I wouldn't make a habit of roaring up the beach with a 20 (it's actually 19' - 6" BTW). Pull the port covers off and you can see daylight at the keel line (if you know what I mean? Kind of translucent there at the seam). You'll definitely want beach wheels for the boat.
We had a blast sailing it, especially in 5 to 12 knots, when other boats were wishing for more wind. Down side is it's a real handful in over 20.
Check out the Hobie Class Social Network
There's a few 20's for sale in the classified.