A "guilty pleasure" is anything that you enjoy but would not necessarily want to admit that you enjoy, or even that you have any familiarity with.
Many of Spelling's shows were lowbrow, classless, aimed at the lowest common denominator. Spelling himself called them "mind candy," implying that they were tasty but worthless.
Given this, many people -- usually the intellectual and/or snobby sort -- would never admit to watching these shows. However, many did, because they enjoyed them.