This mystery features the Three Stooges: Larry, Moe, and Curly-Joe. They were one of two old-time movie teams that were featured on The New Scooby-Doo Movies, along with Laurel and Hardy. Their voices were provided by others, even though Larry Fine, Moe Howard, and Joe DeRita were still alive.
Although The Three Stooges are represented by mimics, this season later featured an authentic Three Stooge - Joe Besser - as guest star Babu in Mystery in Persia (1973).
The jumpsuits worn in this series by Larry, Moe, and Curly-Joe do not resemble anything that the authentic The Three Stooges wore in their films.
Shaggy making a joke about him being a "flour/flower child" is a very rare reference in any Scooby series. Canonically, Shaggy has always been presented as a beatnik, not a hippie. (Part of the reason he's a beatnik was because Hanna-Barbera supposedly wanted to avoid making a political statement with the character.)
While in the desert with Daphne, Fred makes an amusing, but also "sexist" joke: "This desert reminds me of a woman, it goes on and on and on..." Daphne replies with an exasperated comment on "Men!" This is an unusually mature joke for early Scooby-Doo.