Interesting choice. As a kid, I enjoyed watching their cartoon re-reruns, and the first live action movie was...tolerable, the second one not so much. But since then, they've really dropped off of people's radar and its been very, very quiet regarding new product or any news that would make folks clamour for Flintstone back-issues...that's 20 years of virtual silence for a once-mighty franchise.
Additionally, the 1st Flintstones comic was part of a large warehouse find which included many high grade copies so that's also kept a damper on price.
If you like the Flintstones and want to complete a high grade run, its fairly inexpensive, and much easier to achieve than Scooby Doo, but Scooby Doo is just starting to get the recognition it deserves, being on the forefront of Gold Key's (and Marvel, DC, etc) most viable properties over the past 50 years, and it still has a long way to go to hit its true place/pricing in the market