with the hotplate type vaporizers, having a wetter herb actually helps teh vaporizing proscess. as water is a good conductor of heat, and also helps prevent burning of teh plant matter, it tends to heat your pot more evenely, making it more of a vaporizer, and less of a smokerizer.

but then again most vaporizers where the herb is directly on the element arent very good (exept a choice few which use glass elements, and are very well designed. etc)