ocnb12, although I don't use a snorkel in my own diving, I agree with you. The experience of having your face in the water and breathing through the snorkel is a great introduction to what you are going to do in diving -- plus, if you can tolerate the increased dead space of a snorkel, you're unlikely to panic during your first experiences with a regulator. And you can practice mask skills (which are a big stressor for dive students) with a snorkel.
My experiences snorkeling definitely helped prepare me for diving. I just don't think a snorkel is much use once you have a regulator at hand.