The CZ is a great beach machine, compared to many others. It does very well in the wet sand and has respectable depth. It's a little more "skittish" actually IN the water, sometimes falsing a little but it's still decent. The Excal has it beat hands down though in depth and in it's ability to get the small gold and deeper stuff. Because the Excal is a threshold machine, I believe you have a much better chance of hitting a small or deep gold ring with it because a near-miss with the CZ will mean you go right over it. A near-miss with the Excal (or the Quattro for that matter) will more than likely result in a break in the background threshold buzz and that will tip you off to put on the brakes and go back for a closer look. This is the most important reason to choose the Minelabs over the CZ for the beach. And that goes for the Quattro, Explorers, and the Sovereigns as well.
But like the CZ, none of those are waterproof. The CZ is billed as "Rainproof" and "Slash Resistant", not splash PROOF. That means if you want to go (or get caught) hunting in a moderate rain, you'll probably be OK. As for the "Splash Resistant" part, they're talking about salt water there. Which is much more invasive and damaging than fresh water. And so a light splash of it on the display will probably be fine and maybe even be alright if you get nailed by a wave and then get out and rinse/dry it off quickly. But if you drop it in the water, you're screwed. I've seen it happen and it's a cryin' shame.
I don't see the coil switch issue being problem. The 10" coil on the Excal 1000 is big enough to give adequate coverage in the wet and dry and small enough to get in the water. Maybe not as nimble as the 8" or as big coverage as the S-12, but does both well. I say get the 1000 and don't look back. On the other hand, the CZ-70 is a wonderful machine as well and it's a terrific land hunter as well as a capable beach hunter. If you're trips to the beach will be few enough and little enough time in the water to not justify the cost of a water machine AND you have total faith in yourself to not drop it in, then get one. But the 17 frequencies of the Excal and it's variable tone system make it the winner at the beach.