Youtube's being annoying so I'll try and upstage Gaffer here rather than his youtube page. BKEV TO THE RESCUE! The footage is codenamed Zyu2, and someone has kindly uploaded what he knows/believes to be much of said "new" footage on youtube. http://www.youtube.com/user/Zyu2. You'll notice that a few of these videos have only the monsters intact. This is because Saban ingeniously was able to splice in the new megazords from later seasons into these(particularly here Zyu2) shots, by panning away any time one side got hit via a generic reaction shot. Some episodes you never see the Zords clash at all at the same time on-screen.

And define spin-offs... Super Sentai is a yearly thing, where - much like the Power Rangers - you can expect a different series every 1-2 years. Most upgrades, except for the temporary ninja suits from... season 3?, are just more stock footage.