At the risk of coming across as a fashion *BEEP* I must say I love my keens. I have the Newport (google up “keen Newport”) which comes with a full toe box. I have hiked on them on beaches, deserts, young volcanoes full of crunchy lava, old muddy volcanoes, a number of other places, and they have taken the punishment without problems.
They are tough. I’m wearing the soles out but then again, I would have worn the soles out of my old Army boots with the amount of abuse I’m putting them through. The toe box is strong enough to protect your toes from falling rocks. Recently I had a big, sharp rock (30+ pounds) fall on my left foot and while I screamed like a little girl, I don’t want to think how it would have been with an open toe sandal. Through all that the stitches are solid and the materials look as strong as it did when new.
Funny enough, they are at their worst on wet sand. Sand gets in and don’t want to get out. The good news is that they work every bit as well dry or wet, and they dry in no time at all. Their straps are bloody perfect. Once you tighten them up you can confidently run down slopes without worrying about them rubbing your feet the wrong way. I have worn them with socks on chilly days. I know it looks retarded but I stopped worrying about what I looked like a long time ago.
If you can buy/rig some breathable-yet-waterproof sock liners, they might work. Only you know how warm you want to keep your feet.