Eh, I dunno. I'd argue that at least Zombie Island was interesting specifically because it broke the "really mundane explanation" formula. Scooby Doo had always been very formulaic, with every episode revealing why some huckster had been exploiting local superstition for their own benefit, and the gang was as used to this as the audience was. Sure, they'd run around scared, but even Shaggy and Scooby always had their eyes out for the clues that would properly explain everything.
And in Zombie Island the gang and audience were expecting more of the same. It's always some guy in a mask trying to scare the locals in service of some financial con. That's the rule. We get to the unmasking...and we're as surprised as the gang is that it's not a mask, nor is it horrible scarring. It's legitimately a zombie, and that's legitimately shocking in a way that is only possible because we'd been trained to believe that it was an absolute rule that the supernatural did not actually exist in this series. The film's break from tradition had a lot of power specifically because of the contrast, and made it work.