I think Cedric is simply a character people enjoy making fun of, because his role is largely functional and he tends to exaggerate some dangers and completely fail to warn the player about others. Sidekick characters have certain limitations in adventure games and Cedric exhibits most of the downside -- they always seem to be getting in trouble and they rarely really contribute to solving problems, because after all that's the player's job.
But he's actually one of the only non-player characters we really get to know in the whole King's Quest series, so that counts for something. I'd like to see him put in a cameo appearance in the Telltale game.
(I never liked his voice in the CD version of King's Quest V, but that's partially because I had a different voice in my head from playing the non-talkie version first. I still think the high-pitched voice constrained what the character could do acting-wise, but that doesn't mean it's an invalid choice.)