I did not have any of these books as a kid, but I have a VHS tape that featured limited animation videos of Caverns of Fear and Time Trouble that were created using the art from the books. I never liked the video as much as the Filmation Cartoon, but long after the cartoon was off the air, I could still watch that video. I have very vivid memories of the video because I watched it so often. The books do have pretty great art work and feature quite a few different characters from the Eternia.
If you want to see the limited animation version of Caverns of Fear check out the video below.