I got my snorkle for several reasons. First and foremost is that I drive on a lot of real dusty roads. Before the snorkle, on an outing I would have to clean the air filter every day, It got the intake up and away from the heavy dust.
As it turns out I was running it on a 2.5L at the time. It actually added 4mph top speed on the freeway due apparently from the ram air effect.
I have done several water crossings that would have seriously bothered me otherwise. A snorkle by itself does little by itself to keep an engine running in water, there are tons of other things that need to be done as well, but It helps. Anyway, it looks cool.
PS for water crossings, you might want to check your door seals. Generally they suck bigtime.