I actually havent received any spam from this promotion since I first signed up. I believe this promotion is targeted more towards getting people to try the candy bar than to collect email addresses for spamming purposes.
From their privacy policy:
"(b) Get a Coupon: Hershey Foods Corporation will only use this information for mailing your coupon. Data will be kept for a maximum of two weeks and then discarded."
Not to mention that the candy bar will cost you the price of the magazine unless you find it acceptable to "take" it from the newsstand...