Actor Allusion: The casting of Hisashi Sakai as the sixth ranger this season is an allusion to the fact that the year before, he played the sixth ranger's child self.
Hey, It's That Guy!: The supporting cast includes quite a few Choujin Sentai Jetman alumni, namely Yutaka Hirose (Tranza and Jin Matoba), Ikko Tadano (Raita Oishi and the second Kameo), and Mikiko Miki (Chief Aya Odagiri and Ko's mother)
Gaara is Akiko Amamatsuri, who was one of the villains (Dr. Mazenda) in Choujuu Sentai Liveman alongside Yutaka Hirose (Dr. Kemp).
The Other Darrin: Sugisaku Imagawa, the actor who originally played Kameo, left the show for health reasons, so his role was taken over by Ikko Tadano (who previously played Raita in Choujin Sentai Jetman) from Episode 29 and onward. But since Kameo is just a human disguise of Daimugen, why not?
The Other Marty: As shown in the trailer for The Movie, Keiichi Wada (Ryō) and Keisuke Tsuchiya (Kazu) originally had their roles reversed. (The basis for the switch being Wada's actual martial arts skills.)
Prop Recycling: Iron-Face Choryu's armor skirt was originally made for Burai from the previous season.
Recycled Script: Kujaku's subplot has strong similarity to the "Burai's lifespan" plot from the previous season. Seeking magic healing water to restore life-force, close to the end it's revealed it won't help the person and is instead needed for someone else, at the end character dies and ascends. Additionally, the character is vengeance driven at first and causes damage to heroes and villains alike before having some sense knocked into them.