Cupid in "Terrible Love" is Jerry Russo (meaning that this isn't the first time David DeLuise worked on a kids' show with supernatural elements in it).
Stuart (the nerd who ends up tricking Maggie into getting hit with Cupid's arrow played by Nick Purcha) would later go on to be Watch on Spooksville (another horror kids' series that airs on The Hub).
Tom Kenny is the title character on the episode "Uncle Howee" (and also voices the rabbit puppet, Loomis).
Charleotte McClainor Chyna Parks if you prefer played Sam on the episode "Argh V" (about a responsible girl whose free-wheeling parents buy an RV that belonged to a family that died in a crash and the RV is possessed by their spirits).
One of the main characters in "Dreamcatcher"note The one about girls at summer camp trying to stop a spider creature that feeds off nightmares is played by Michelle Creber (which any brony worth his salt would know is the voice of Apple Bloom on both My Little Pony: Friendship Is Magic and Equestria Girls).
Another My Little Pony: Friendship is Magic voice actress on an episode of The Haunting Hour: Alice's mother in "My Old House" voices Princess Celestia.
Gorgonzola (Will Shadley) plays Aaron in "Spaceman".
Uncle Howee and Loomis the rabbit are voiced by Tom Kenny (SpongeBob SquarePants, The Ice King and other characters, but SpongeBob and the Ice King are the most popular).
Jeff (the square-headed kid) is Sean (Sean Giambrone) in the season four premiere episode "I'm Not Martin". It's not hard to figure out (unless you've never seen Clarence), since Sean sounds like Jeff when he yells, "I'm not Martin!" (which is often in this episode).
Keep Circulating the Tapes: Zigzagged. Seasons one and two are available on Netflix (and the show has episodes released on DVD), but the episode "Scarecrow" has the ending where Bobby is turned into a scarecrow along with the scarecrow salesman instead of the one where Bobby burns the scarecrow salesman after he reverts to his original form. If you want to see "Scarecrow" with the "Bobby burns the scarecrow salesman's original form, then walks off into the empty world" ending, then you'll have to comb through the Internet for it. As for the episodes from seasons three (both part onenote from "Grampires" to "Terrible Love" and part twonote from "Seance" to "Uncle Howee") and four, then you'll have to settle for torrent downloading for most of them and video website viewing for the rest, as those episodes haven't been released on DVD yet and Discovery Family doesn't rerun the show anymore.
Screwed by the Network: In spades. Despite being a very popular show, having amazing ratings, and even plans for a fifth season (or sixth, if you believe part two of season three is a separate season), The Hub changing over to Discovery Family pretty much killed this show's chance of ever continuing. After the Christmas Episode "Goodwill Toward Men," the series was taken off the schedule and R.L. Stine himself said on his Twitter that the show was canceled and no new episodes were going to be made.
Talking to Himself: As mentioned above, Tom Kenny not only plays Uncle Howee on the episode of the same name, but is also the voice of the rabbit puppet, Loomis, and they interact with each other throughout the episode.
Why Fandom Can't Have Nice Things: In-Universe example with Brush With Madness: Alan Miller became a Reclusive Artist after being stalked by a homicidal fan eight years prior to the episode's story and snapped at Corey because he foolishly said "I follow you on Twitter" (though why a reclusive artist would be on a social media site like Twitter is a mystery).