Thank goodness for Netflix. I doubt there's very many Power Rangers titles I'd actually want to own.
The 90's movies.
The reboot movie.
Maybe a little bit of the Mighty Morphin era, depending on if the DVD/Blurays extras have those bonus music videos from the VHS days. ("Fight", "I Will Win", "We Need A Hero", etc.)
But that's about it, really. It's more for history purposes, and for the titles that didn't rely on any Japanese resources.