I forgot where I read it, so I don't have anything to back up my following statements. Just take it for what it's worth.
When developing the initial Scooby concept, several ideas were tossed around. One was that the teens would be musicians, but then considered that might be too much to juggle in the episodes. Later series (not Scooby shows) would employ that bit after all. Of greater import would be the role of the dog. One idea was to make him large but cowardly, the Scooby we actually got. The other was the opposite, a pocket sized mutt that wouldn't back down, basically Scrappy.
Funny how all those ideas wound up being used one way or another.
For all its debated faults, at least the animated Trek did NOT force a cute mascot comic relief character upon us. If that had happened, I don't think there'd be ANY debate whether or not Kirk and company had those missions! Fans would demand the master negatives be burned!